xref: /macosx-10.10.1/libmalloc-53.1.1/src/magazine_malloc.c

/*
 * Copyright (c) 1999, 2006, 2008 Apple Inc. All rights reserved.
 *
 * @APPLE_LICENSE_HEADER_START@
 *
 * This file contains Original Code and/or Modifications of Original Code
 * as defined in and that are subject to the Apple Public Source License
 * Version 2.0 (the 'License'). You may not use this file except in
 * compliance with the License. Please obtain a copy of the License at
 * http://www.opensource.apple.com/apsl/ and read it before using this
 * file.
 *
 * The Original Code and all software distributed under the License are
 * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
 * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
 * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
 * Please see the License for the specific language governing rights and
 * limitations under the License.
 *
 * @APPLE_LICENSE_HEADER_END@
 */

/* Author: Bertrand Serlet, August 1999 */

/*
 Multithread enhancements for "tiny" allocations introduced February 2008.
 These are in the spirit of "Hoard". See:
 Berger, E.D.; McKinley, K.S.; Blumofe, R.D.; Wilson, P.R. (2000).
 "Hoard: a scalable memory allocator for multithreaded applications".
 ACM SIGPLAN Notices 35 (11): 117-128. Berger2000.
 <http://portal.acm.org/citation.cfm?id=356989.357000>
 Retrieved on 2008-02-22.
 */

/* gcc -g -O3 magazine_malloc.c malloc.c -o libmagmalloc.dylib -I. \
 -I/System/Library/Frameworks/System.framework/PrivateHeaders/ -funit-at-a-time \
 -dynamiclib -Wall -arch x86_64 -arch i386 -arch ppc */

#include <TargetConditionals.h>

#include "scalable_malloc.h"
#include "malloc_printf.h"
#include "malloc_internal.h"
#include "magmallocProvider.h"

#include <_simple.h>
#include <errno.h>
#include <signal.h>
#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <libkern/OSAtomic.h>
#include <mach/vm_statistics.h>
#include <mach/mach_init.h>
#include <os/tsd.h>
#include <sys/types.h>
#include <sys/mman.h>
#include <sys/param.h>

#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__arm64__)
#define __APPLE_API_PRIVATE
#include <machine/cpu_capabilities.h>
#define _COMM_PAGE_VERSION_REQD 9
#undef __APPLE_API_PRIVATE
#else
#include <sys/sysctl.h>
#endif

#include <libkern/OSAtomic.h>
#include <mach-o/dyld.h>	/* for NSVersionOfLinkTimeLibrary() */
#include <mach-o/dyld_priv.h>	/* for _dyld_get_image_slide() */
#include <crt_externs.h>	/* for _NSGetMachExecuteHeader() */
#include <mach/vm_param.h>
#include <mach/mach_vm.h>
#include <sys/vmparam.h>
#include <os/tsd.h>

#include <mach/vm_page_size.h>

#define trunc_page_quanta(x) (vm_page_size >= vm_kernel_page_size ? trunc_page((x)) : trunc_page_kernel((x)))
#define round_page_quanta(x) (vm_page_size >= vm_kernel_page_size ? round_page((x)) : round_page_kernel((x)))
#define vm_page_quanta_size MAX(vm_page_size, vm_kernel_page_size)
#define vm_page_quanta_shift MAX(vm_page_shift, vm_kernel_page_shift)

#ifndef PAGE_MAX_SIZE
/* Until xnu exposes these publically in mach/vm_param.h ... */

#define PAGE_MAX_SHIFT      14
#define PAGE_MAX_SIZE       (1 << PAGE_MAX_SHIFT)
#define PAGE_MAX_MASK       (PAGE_MAX_SIZE-1)

#define PAGE_MIN_SHIFT      12
#define PAGE_MIN_SIZE       (1 << PAGE_MIN_SHIFT)
#define PAGE_MIN_MASK       (PAGE_MIN_MASK-1)

#endif

#include <CrashReporterClient.h>

/*********************	DEFINITIONS	************************/

#define DEBUG_MALLOC			0 // set to one to debug malloc itself

#define DEBUG_CLIENT			0 // set to one to debug malloc client

#define DEBUG_MADVISE			0

// <rdar://problem/10397726>
#define RELAXED_INVARIANT_CHECKS 1

#if TARGET_OS_EMBEDDED
# define MADVISE_PRESSURE_RELIEF 0
#else
// <rdar://problem/12596555>
# define MADVISE_PRESSURE_RELIEF 1
#endif

#if DEBUG_MALLOC
#warning DEBUG_MALLOC ENABLED
# define INLINE
# define ALWAYSINLINE
# define CHECK_MAGAZINE_PTR_LOCKED(szone, mag_ptr, fun)				\
	do {										\
		if (TRY_LOCK(mag_ptr->magazine_lock)) {			\
			malloc_printf("*** magazine_lock was not set %p in %s\n",		\
			mag_ptr->magazine_lock, fun);						\
		}										\
	} while (0)
#else
# define INLINE	__inline__
# define ALWAYSINLINE __attribute__((always_inline))
# define CHECK_MAGAZINE_PTR_LOCKED(szone, mag_ptr, fun)	{}
#endif

# define NOINLINE __attribute__((noinline))

#if defined(__i386__) || defined(__x86_64__)
#define CACHE_LINE 128 /* Future-proofing at 128B */
#elif defined(__arm__) || defined(__arm64__)
#define CACHE_LINE 64
#else
#define CACHE_LINE 32
#endif
#define CACHE_ALIGN __attribute__ ((aligned (CACHE_LINE) ))

#if !__LP64__
#define ASLR_INTERNAL			1
#endif

#define SCRIBBLE_BYTE			0xaa /* allocated scribble */
#define SCRABBLE_BYTE			0x55 /* free()'d scribble */
#define SCRUBBLE_BYTE			0xdd /* madvise(..., MADV_FREE) scriblle */

/*
 * msize - a type to refer to the number of quanta of a tiny or small
 * allocation.  A tiny block with an msize of 3 would be 3 << SHIFT_TINY_QUANTUM
 * bytes in size.
 */
typedef unsigned short msize_t;

typedef union {
	void	*p;
	uintptr_t	u;
} ptr_union;

typedef struct {
	ptr_union	previous;
	ptr_union	next;
} free_list_t;

typedef unsigned int grain_t; // N.B. wide enough to index all free slots

typedef int mag_index_t;

#define CHECK_REGIONS			(1 << 31)
#define DISABLE_ASLR			(1 << 30)

#define MAX_RECORDER_BUFFER		256

/*********************	DEFINITIONS for tiny	************************/

/*
 * Memory in the Tiny range is allocated from regions (heaps) pointed to by the
 * szone's hashed_regions pointer.
 *
 * Each region is laid out as a heap, followed by a header block, all within
 * a 1MB (2^20) block.  This means there are 64520 16-byte blocks and the header
 * is 16138 bytes, making the total 1048458 bytes, leaving 118 bytes unused.
 *
 * The header block is arranged as in struct tiny_region defined just below, and
 * consists of two bitfields (or bit arrays) interleaved 32 bits by 32 bits.
 *
 * Each bitfield comprises NUM_TINY_BLOCKS bits, and refers to the corresponding
 * TINY_QUANTUM block within the heap.
 *
 * The bitfields are used to encode the state of memory within the heap.  The header bit indicates
 * that the corresponding quantum is the first quantum in a block (either in use or free).  The
 * in-use bit is set for the header if the block has been handed out (allocated).  If the header
 * bit is not set, the in-use bit is invalid.
 *
 * The szone maintains an array of NUM_TINY_SLOTS freelists, each of which is used to hold
 * free objects of the corresponding quantum size.
 *
 * A free block is laid out depending on its size, in order to fit all free
 * blocks in 16 bytes, on both 32 and 64 bit platforms.  One quantum blocks do
 * not store their size in the block, instead relying on the header information
 * to determine their size.  Blocks of two or more quanta have room to store
 * their size in the block, and store it both after the 'next' pointer, and in
 * the last 2 bytes of the block.
 *
 * 1-quantum block
 * Offset (32-bit mode)	(64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * end          end
 *
 * >1-quantum block
 * Offset (32-bit mode)	(64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * 0x8          0x10     : size (in quantum counts)
 * end - 2      end - 2  : size (in quantum counts)
 * end          end
 *
 * All fields are pointer-sized, except for the size which is an unsigned short.
 *
 */

#define SHIFT_TINY_QUANTUM		4	// Required for AltiVec
#define	TINY_QUANTUM			(1 << SHIFT_TINY_QUANTUM)

#define FOLLOWING_TINY_PTR(ptr,msize)	(((unsigned char *)(ptr)) + ((msize) << SHIFT_TINY_QUANTUM))

#ifdef __LP64__
#define NUM_TINY_SLOTS			64	// number of slots for free-lists
#else
#define NUM_TINY_SLOTS			32	// number of slots for free-lists
#endif

#define NUM_TINY_BLOCKS			64520
#define SHIFT_TINY_CEIL_BLOCKS		16 // ceil(log2(NUM_TINY_BLOCKS))
#define NUM_TINY_CEIL_BLOCKS		(1 << SHIFT_TINY_CEIL_BLOCKS)
#define TINY_BLOCKS_ALIGN		(SHIFT_TINY_CEIL_BLOCKS + SHIFT_TINY_QUANTUM) // 20

#define TINY_ENTROPY_BITS		15
#define TINY_ENTROPY_MASK		((1 << TINY_ENTROPY_BITS) - 1)

/*
 * Avoid having so much entropy that the end of a valid tiny allocation
 * might overrun the end of the tiny region.
 */
#if TINY_ENTROPY_MASK + NUM_TINY_SLOTS > NUM_TINY_BLOCKS
#error Too many entropy bits for tiny region requested
#endif

/*
 * Enough room for the data, followed by the bit arrays (2-bits per block)
 * plus rounding to the nearest page.
 */
#define CEIL_NUM_TINY_BLOCKS_WORDS	(((NUM_TINY_BLOCKS + 31) & ~31) >> 5)
#define TINY_METADATA_SIZE		(sizeof(region_trailer_t) + sizeof(tiny_header_inuse_pair_t) * CEIL_NUM_TINY_BLOCKS_WORDS)
#define TINY_REGION_SIZE							\
	((NUM_TINY_BLOCKS * TINY_QUANTUM + TINY_METADATA_SIZE + PAGE_MAX_SIZE - 1) & ~ (PAGE_MAX_SIZE - 1))

#define TINY_METADATA_START		(NUM_TINY_BLOCKS * TINY_QUANTUM)

/*
 * Beginning and end pointers for a region's heap.
 */
#define TINY_REGION_ADDRESS(region)	((void *)(region))
#define TINY_REGION_END(region)		((void *)(((uintptr_t)(region)) + (NUM_TINY_BLOCKS * TINY_QUANTUM)))

/*
 * Locate the heap base for a pointer known to be within a tiny region.
 */
#define TINY_REGION_FOR_PTR(_p)		((void *)((uintptr_t)(_p) & ~((1 << TINY_BLOCKS_ALIGN) - 1)))

/*
 * Convert between byte and msize units.
 */
#define TINY_BYTES_FOR_MSIZE(_m)	((_m) << SHIFT_TINY_QUANTUM)
#define TINY_MSIZE_FOR_BYTES(_b)	((_b) >> SHIFT_TINY_QUANTUM)

#ifdef __LP64__
# define TINY_FREE_SIZE(ptr)		(((msize_t *)(ptr))[8])
#else
# define TINY_FREE_SIZE(ptr)		(((msize_t *)(ptr))[4])
#endif
#define TINY_PREVIOUS_MSIZE(ptr)	((msize_t *)(ptr))[-1]

/*
 * Layout of a tiny region
 */
typedef uint32_t tiny_block_t[4]; // assert(TINY_QUANTUM == sizeof(tiny_block_t))

typedef struct tiny_header_inuse_pair
{
	uint32_t	header;
	uint32_t	inuse;
} tiny_header_inuse_pair_t;

typedef struct region_trailer
{
	struct region_trailer	*prev;
	struct region_trailer	*next;
	boolean_t			recirc_suitable;
	volatile int		pinned_to_depot;
	unsigned			bytes_used;
	mag_index_t			mag_index;
} region_trailer_t;

typedef struct tiny_region
{
	tiny_block_t blocks[NUM_TINY_BLOCKS];

	region_trailer_t trailer;

	// The interleaved bit arrays comprising the header and inuse bitfields.
	// The unused bits of each component in the last pair will be initialized to sentinel values.
	tiny_header_inuse_pair_t pairs[CEIL_NUM_TINY_BLOCKS_WORDS];

	uint8_t pad[TINY_REGION_SIZE - (NUM_TINY_BLOCKS * sizeof(tiny_block_t)) - TINY_METADATA_SIZE];
} *tiny_region_t;

/*
 * Per-region meta data for tiny allocator
 */
#define REGION_TRAILER_FOR_TINY_REGION(r)	(&(((tiny_region_t)(r))->trailer))
#define MAGAZINE_INDEX_FOR_TINY_REGION(r)	(REGION_TRAILER_FOR_TINY_REGION(r)->mag_index)
#define BYTES_USED_FOR_TINY_REGION(r)		(REGION_TRAILER_FOR_TINY_REGION(r)->bytes_used)

/*
 * Locate the block header for a pointer known to be within a tiny region.
 */
#define TINY_BLOCK_HEADER_FOR_PTR(_p)	((void *)&(((tiny_region_t)TINY_REGION_FOR_PTR(_p))->pairs))

/*
 * Locate the inuse map for a given block header pointer.
 */
#define TINY_INUSE_FOR_HEADER(_h)	((void *)&(((tiny_header_inuse_pair_t *)(_h))->inuse))

/*
 * Compute the bitmap index for a pointer known to be within a tiny region.
 */
#define TINY_INDEX_FOR_PTR(_p) 		(((uintptr_t)(_p) >> SHIFT_TINY_QUANTUM) & (NUM_TINY_CEIL_BLOCKS - 1))

#define TINY_CACHE			1	// This governs a last-free cache of 1 that bypasses the free-list

#if ! TINY_CACHE
#warning TINY_CACHE turned off
#endif

#define TINY_REGION_PAYLOAD_BYTES	(NUM_TINY_BLOCKS * TINY_QUANTUM)

/*********************	DEFINITIONS for small	************************/

/*
 * Memory in the Small range is allocated from regions (heaps) pointed to by the szone's hashed_regions
 * pointer.
 *
 * Each region is laid out as a heap, followed by the metadata array, all within an 8MB (2^23) block.
 * The array is arranged as an array of shorts, one for each SMALL_QUANTUM in the heap.
 * This means there are 16320 512-blocks and the array is 16320*2 bytes, which totals 8388480, leaving
 * 128 bytes unused.
 *
 * The MSB of each short is set for the first quantum in a free block.  The low 15 bits encode the
 * block size (in SMALL_QUANTUM units), or are zero if the quantum is not the first in a block.
 *
 * The szone maintains an array of 32 freelists, each of which is used to hold free objects
 * of the corresponding quantum size.
 *
 * A free block is laid out as:
 *
 * Offset (32-bit mode)	(64-bit mode)
 * 0x0          0x0      : previous
 * 0x4          0x08     : next
 * 0x8          0x10     : size (in quantum counts)
 * end - 2	end - 2  : size (in quantum counts)
 * end		end
 *
 * All fields are pointer-sized, except for the size which is an unsigned short.
 *
 */

#define SMALL_IS_FREE			(1 << 15)

#define	SHIFT_SMALL_QUANTUM		(SHIFT_TINY_QUANTUM + 5)	// 9
#define	SMALL_QUANTUM			(1 << SHIFT_SMALL_QUANTUM)	// 512 bytes

#define FOLLOWING_SMALL_PTR(ptr,msize)	(((unsigned char *)(ptr)) + ((msize) << SHIFT_SMALL_QUANTUM))

/*
 * The number of slots in the free-list for small blocks.  To avoid going to
 * vm system as often on large memory machines, increase the number of free list
 * spots above some amount of RAM installed in the system.
 */
#define NUM_SMALL_SLOTS			32
#define NUM_SMALL_SLOTS_LARGEMEM	256
#define SMALL_BITMAP_WORDS		8

/*
 * We can only represent up to 1<<15 for msize; but we choose to stay even below that to avoid the
 * convention msize=0 => msize = (1<<15)
 */
#define NUM_SMALL_BLOCKS		16320
#define SHIFT_SMALL_CEIL_BLOCKS		14 // ceil(log2(NUM_SMALL_BLOCKs))
#define NUM_SMALL_CEIL_BLOCKS		(1 << SHIFT_SMALL_CEIL_BLOCKS)
#define SMALL_BLOCKS_ALIGN		(SHIFT_SMALL_CEIL_BLOCKS + SHIFT_SMALL_QUANTUM) // 23

#define SMALL_ENTROPY_BITS		13
#define SMALL_ENTROPY_MASK		((1 << SMALL_ENTROPY_BITS) - 1)

/*
 * Avoid having so much entropy that the end of a valid small allocation
 * might overrun the end of the small region.
 */
#if SMALL_ENTROPY_MASK + NUM_SMALL_SLOTS > NUM_SMALL_BLOCKS
#error Too many entropy bits for small region requested
#endif

#define SMALL_METADATA_SIZE		(sizeof(region_trailer_t) + NUM_SMALL_BLOCKS * sizeof(msize_t))
#define SMALL_REGION_SIZE						\
	((NUM_SMALL_BLOCKS * SMALL_QUANTUM + SMALL_METADATA_SIZE + PAGE_MAX_SIZE - 1) & ~ (PAGE_MAX_SIZE - 1))

#define SMALL_METADATA_START		(NUM_SMALL_BLOCKS * SMALL_QUANTUM)

/*
 * Beginning and end pointers for a region's heap.
 */
#define SMALL_REGION_ADDRESS(region)	((unsigned char *)region)
#define SMALL_REGION_END(region)	(SMALL_REGION_ADDRESS(region) + (NUM_SMALL_BLOCKS * SMALL_QUANTUM))

/*
 * Locate the heap base for a pointer known to be within a small region.
 */
#define SMALL_REGION_FOR_PTR(_p)	((void *)((uintptr_t)(_p) & ~((1 << SMALL_BLOCKS_ALIGN) - 1)))

/*
 * Convert between byte and msize units.
 */
#define SMALL_BYTES_FOR_MSIZE(_m)	((_m) << SHIFT_SMALL_QUANTUM)
#define SMALL_MSIZE_FOR_BYTES(_b)	((_b) >> SHIFT_SMALL_QUANTUM)

#define SMALL_PREVIOUS_MSIZE(ptr)	((msize_t *)(ptr))[-1]

/*
 * Layout of a small region
 */
typedef uint32_t small_block_t[SMALL_QUANTUM/sizeof(uint32_t)];

typedef struct small_region
{
	small_block_t blocks[NUM_SMALL_BLOCKS];

	region_trailer_t trailer;

	msize_t small_meta_words[NUM_SMALL_BLOCKS];

	uint8_t pad[SMALL_REGION_SIZE - (NUM_SMALL_BLOCKS * sizeof(small_block_t)) - SMALL_METADATA_SIZE];
} *small_region_t;

/*
 * Per-region meta data for small allocator
 */
#define REGION_TRAILER_FOR_SMALL_REGION(r)	(&(((small_region_t)(r))->trailer))
#define MAGAZINE_INDEX_FOR_SMALL_REGION(r)	(REGION_TRAILER_FOR_SMALL_REGION(r)->mag_index)
#define BYTES_USED_FOR_SMALL_REGION(r)		(REGION_TRAILER_FOR_SMALL_REGION(r)->bytes_used)

/*
 * Locate the metadata base for a pointer known to be within a small region.
 */
#define SMALL_META_HEADER_FOR_PTR(_p)	(((small_region_t)SMALL_REGION_FOR_PTR(_p))->small_meta_words)

/*
 * Compute the metadata index for a pointer known to be within a small region.
 */
#define SMALL_META_INDEX_FOR_PTR(_p)	(((uintptr_t)(_p) >> SHIFT_SMALL_QUANTUM) & (NUM_SMALL_CEIL_BLOCKS - 1))

/*
 * Find the metadata word for a pointer known to be within a small region.
 */
#define SMALL_METADATA_FOR_PTR(_p)	(SMALL_META_HEADER_FOR_PTR(_p) + SMALL_META_INDEX_FOR_PTR(_p))

/*
 * Determine whether a pointer known to be within a small region points to memory which is free.
 */
#define SMALL_PTR_IS_FREE(_p)		(*SMALL_METADATA_FOR_PTR(_p) & SMALL_IS_FREE)

/*
 * Extract the msize value for a pointer known to be within a small region.
 */
#define SMALL_PTR_SIZE(_p)		(*SMALL_METADATA_FOR_PTR(_p) & ~SMALL_IS_FREE)

#define SMALL_CACHE			1
#if !SMALL_CACHE
#warning SMALL_CACHE turned off
#endif

#define SMALL_REGION_PAYLOAD_BYTES	(NUM_SMALL_BLOCKS * SMALL_QUANTUM)

/*************************  DEFINITIONS for large  ****************************/

#define LARGE_THRESHOLD			(15 * 1024) // strictly above this use "large"
#define LARGE_THRESHOLD_LARGEMEM	(127 * 1024)

#if (LARGE_THRESHOLD > NUM_SMALL_SLOTS * SMALL_QUANTUM)
#error LARGE_THRESHOLD should always be less than NUM_SMALL_SLOTS * SMALL_QUANTUM
#endif

#if (LARGE_THRESHOLD_LARGEMEM > NUM_SMALL_SLOTS_LARGEMEM * SMALL_QUANTUM)
#error LARGE_THRESHOLD_LARGEMEM should always be less than NUM_SMALL_SLOTS * SMALL_QUANTUM
#endif

/*
 * When all memory is touched after a copy, vm_copy() is always a lose
 * But if the memory is only read, vm_copy() wins over memmove() at 3 or 4 pages
 * (on a G3/300MHz)
 *
 * This must be larger than LARGE_THRESHOLD
 */
#define VM_COPY_THRESHOLD		(40 * 1024)
#define VM_COPY_THRESHOLD_LARGEMEM	(128 * 1024)

typedef struct {
	vm_address_t address;
	vm_size_t size;
	boolean_t did_madvise_reusable;
} large_entry_t;

#if !TARGET_OS_EMBEDDED
#define LARGE_CACHE			1
#else
#define LARGE_CACHE			0
#endif
#if !LARGE_CACHE
#warning LARGE_CACHE turned off
#endif
#if defined(__LP64__)
#define LARGE_ENTRY_CACHE_SIZE 16
#define LARGE_CACHE_SIZE_LIMIT ((vm_size_t)0x80000000) /* 2Gb */
#else
#define LARGE_ENTRY_CACHE_SIZE 8
#define LARGE_CACHE_SIZE_LIMIT ((vm_size_t)0x02000000) /* 32Mb */
#endif
#define LARGE_CACHE_SIZE_ENTRY_LIMIT (LARGE_CACHE_SIZE_LIMIT/LARGE_ENTRY_CACHE_SIZE)

#define SZONE_FLOTSAM_THRESHOLD_LOW  (1024 * 512)
#define SZONE_FLOTSAM_THRESHOLD_HIGH (1024 * 1024)

/*******************************************************************************
 * Definitions for region hash
 ******************************************************************************/

typedef void * region_t;
typedef region_t * rgnhdl_t; /* A pointer into hashed_regions array. */

#define INITIAL_NUM_REGIONS_SHIFT	6 // log2(INITIAL_NUM_REGIONS)
#define INITIAL_NUM_REGIONS		(1 << INITIAL_NUM_REGIONS_SHIFT) // Must be a power of 2!
#define HASHRING_OPEN_ENTRY		((region_t) 0) // Initial value and sentinel marking end of collision chain
#define HASHRING_REGION_DEALLOCATED	((region_t)-1) // Region at this slot reclaimed by OS
#define HASH_BLOCKS_ALIGN		TINY_BLOCKS_ALIGN // MIN( TINY_BLOCKS_ALIGN, SMALL_BLOCKS_ALIGN, ... )

typedef struct region_hash_generation {
	size_t		num_regions_allocated;
	size_t		num_regions_allocated_shift; // log2(num_regions_allocated)
	region_t		*hashed_regions;  // hashed by location
	struct		region_hash_generation *nextgen;
} region_hash_generation_t;

/*******************************************************************************
 * Per-processor magazine for tiny and small allocators
 ******************************************************************************/

typedef struct {			// vm_allocate()'d, so the array of magazines is page-aligned to begin with.
	// Take magazine_lock first,  Depot lock when needed for recirc, then szone->{tiny,small}_regions_lock when needed for alloc
	_malloc_lock_s		magazine_lock CACHE_ALIGN;
	// Protection for the crtical section that does allocate_pages outside the magazine_lock
	volatile boolean_t	alloc_underway;

	// One element deep "death row", optimizes malloc/free/malloc for identical size.
	void		*mag_last_free; // low SHIFT_{TINY,SMALL}_QUANTUM bits indicate the msize
	region_t		mag_last_free_rgn; // holds the region for mag_last_free

	free_list_t		*mag_free_list[256]; // assert( 256 >= MAX( NUM_TINY_SLOTS, NUM_SMALL_SLOTS_LARGEMEM ))
	unsigned		mag_bitmap[8]; // assert( sizeof(mag_bitmap) << 3 >= sizeof(mag_free_list)/sizeof(free_list_t) )

	// the first and last free region in the last block are treated as big blocks in use that are not accounted for
	size_t		mag_bytes_free_at_end;
	size_t		mag_bytes_free_at_start;
	region_t		mag_last_region; // Valid iff mag_bytes_free_at_end || mag_bytes_free_at_start > 0

	// bean counting ...
	unsigned		mag_num_objects;
	size_t		mag_num_bytes_in_objects;
	size_t		num_bytes_in_magazine;

	// recirculation list -- invariant: all regions owned by this magazine that meet the emptiness criteria
	// are located nearer to the head of the list than any region that doesn't satisfy that criteria.
	// Doubly linked list for efficient extraction.
	unsigned		recirculation_entries;
	region_trailer_t	*firstNode;
	region_trailer_t	*lastNode;

	uintptr_t		pad[50-CACHE_LINE/sizeof(uintptr_t)];
} magazine_t;

#ifdef __has_extension
#if __has_extension(c_static_assert)
#if __LP64__
_Static_assert(sizeof(magazine_t) == 2560, "Incorrect padding in magazine_t");
#else
_Static_assert(sizeof(magazine_t) == 1280, "Incorrect padding in magazine_t");
#endif
#endif
#endif

#define TINY_MAX_MAGAZINES		32 /* MUST BE A POWER OF 2! */
#define TINY_MAGAZINE_PAGED_SIZE						\
(((sizeof(magazine_t) * (TINY_MAX_MAGAZINES + 1)) + vm_page_quanta_size - 1) &\
~ (vm_page_quanta_size - 1)) /* + 1 for the Depot */

#define SMALL_MAX_MAGAZINES		32 /* MUST BE A POWER OF 2! */
#define SMALL_MAGAZINE_PAGED_SIZE						\
(((sizeof(magazine_t) * (SMALL_MAX_MAGAZINES + 1)) + vm_page_quanta_size - 1) &\
~ (vm_page_quanta_size - 1)) /* + 1 for the Depot */

#define DEPOT_MAGAZINE_INDEX		-1

/****************************** zone itself ***********************************/

/*
 * Note that objects whose adddress are held in pointers here must be pursued
 * individually in the {tiny,small}_in_use_enumeration() routines. See for
 * example the treatment of region_hash_generation and tiny_magazines below.
 */

typedef struct szone_s {				// vm_allocate()'d, so page-aligned to begin with.
	malloc_zone_t		basic_zone;		// first page will be given read-only protection
	uint8_t			pad[PAGE_MAX_SIZE - sizeof(malloc_zone_t)];

	unsigned long		cpu_id_key;		// unused
	// remainder of structure is R/W (contains no function pointers)
	unsigned			debug_flags;
	void			*log_address;

	/* Regions for tiny objects */
	_malloc_lock_s	tiny_regions_lock CACHE_ALIGN;
	size_t			num_tiny_regions;
	size_t			num_tiny_regions_dealloc;
	region_hash_generation_t	*tiny_region_generation;
	region_hash_generation_t	trg[2];

	int				num_tiny_magazines;
	unsigned			num_tiny_magazines_mask;
	int				num_tiny_magazines_mask_shift;
	magazine_t			*tiny_magazines; // array of per-processor magazines

	uintptr_t			last_tiny_advise;

	/* Regions for small objects */
	_malloc_lock_s	small_regions_lock CACHE_ALIGN;
	size_t			num_small_regions;
	size_t			num_small_regions_dealloc;
	region_hash_generation_t	*small_region_generation;
	region_hash_generation_t	srg[2];

	unsigned			num_small_slots; // determined by physmem size

	int				num_small_magazines;
	unsigned			num_small_magazines_mask;
	int				num_small_magazines_mask_shift;
	magazine_t			*small_magazines; // array of per-processor magazines

	uintptr_t			last_small_advise;

	/* large objects: all the rest */
	_malloc_lock_s		large_szone_lock CACHE_ALIGN; // One customer at a time for large
	unsigned			num_large_objects_in_use;
	unsigned			num_large_entries;
	large_entry_t		*large_entries; // hashed by location; null entries don't count
	size_t			num_bytes_in_large_objects;

#if LARGE_CACHE
	int				large_entry_cache_oldest;
	int				large_entry_cache_newest;
	large_entry_t		large_entry_cache[LARGE_ENTRY_CACHE_SIZE]; // "death row" for large malloc/free
	boolean_t			large_legacy_reset_mprotect;
	size_t			large_entry_cache_reserve_bytes;
	size_t			large_entry_cache_reserve_limit;
	size_t			large_entry_cache_bytes; // total size of death row, bytes
#endif

	/* flag and limits pertaining to altered malloc behavior for systems with
	 large amounts of physical memory */
	unsigned  is_largemem;
	unsigned  large_threshold;
	unsigned  vm_copy_threshold;

	/* security cookie */
	uintptr_t cookie;

	/* Initial region list */
	region_t			initial_tiny_regions[INITIAL_NUM_REGIONS];
	region_t			initial_small_regions[INITIAL_NUM_REGIONS];

	/* The purgeable zone constructed by create_purgeable_zone() would like to hand off tiny and small
	 * allocations to the default scalable zone. Record the latter as the "helper" zone here. */
	struct szone_s		*helper_zone;

	boolean_t			flotsam_enabled;
} szone_t;

#define SZONE_PAGED_SIZE		round_page_quanta((sizeof(szone_t)))

#if DEBUG_MALLOC || DEBUG_CLIENT
static void		szone_sleep(void);
#endif
extern void malloc_error_break(void);

// msg prints after fmt, ...
static NOINLINE void	szone_error(szone_t *szone, int is_corruption, const char *msg, const void *ptr, const char *fmt, ...)
__printflike(5, 6);

static void		protect(void *address, size_t size, unsigned protection, unsigned debug_flags);
static void		*allocate_pages(szone_t *szone, size_t size, unsigned char align, unsigned debug_flags,
								int vm_page_label);
static void		*allocate_pages_securely(szone_t *szone, size_t size, unsigned char align,
										 int vm_page_label);
static void		deallocate_pages(szone_t *szone, void *addr, size_t size, unsigned debug_flags);
static int		madvise_free_range(szone_t *szone, region_t r, uintptr_t pgLo, uintptr_t pgHi, uintptr_t *last);
static kern_return_t	_szone_default_reader(task_t task, vm_address_t address, vm_size_t size, void **ptr);

static INLINE		mag_index_t mag_get_thread_index(szone_t *szone) ALWAYSINLINE;
static magazine_t	*mag_lock_zine_for_region_trailer(szone_t *szone, magazine_t *magazines, region_trailer_t *trailer,
													  mag_index_t mag_index);

static INLINE rgnhdl_t	hash_lookup_region_no_lock(region_t *regions, size_t num_entries, size_t shift, region_t r)
ALWAYSINLINE;
static void		hash_region_insert_no_lock(region_t *regions, size_t num_entries, size_t shift, region_t r);
static region_t		*hash_regions_alloc_no_lock(szone_t *szone, size_t num_entries);
static region_t		*hash_regions_grow_no_lock(szone_t *szone, region_t *regions, size_t old_size,
											   size_t *mutable_shift, size_t *new_size);

static INLINE uintptr_t free_list_gen_checksum(uintptr_t ptr) ALWAYSINLINE;
static INLINE uintptr_t free_list_checksum_ptr(szone_t *szone, void *p) ALWAYSINLINE;
static INLINE void	*free_list_unchecksum_ptr(szone_t *szone, ptr_union *ptr) ALWAYSINLINE;
static unsigned		free_list_count(szone_t *szone, free_list_t *ptr);

static INLINE void	recirc_list_extract(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node) ALWAYSINLINE;
static INLINE void	recirc_list_splice_last(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node) ALWAYSINLINE;
static INLINE void	recirc_list_splice_first(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node) ALWAYSINLINE;

static INLINE void	BITARRAY_SET(uint32_t *bits, msize_t index) ALWAYSINLINE;
static INLINE void	BITARRAY_CLR(uint32_t *bits, msize_t index) ALWAYSINLINE;
static INLINE boolean_t BITARRAY_BIT(uint32_t *bits, msize_t index) ALWAYSINLINE;

static msize_t		get_tiny_free_size(const void *ptr);
static msize_t		get_tiny_previous_free_msize(const void *ptr);
static INLINE msize_t	get_tiny_meta_header(const void *ptr, boolean_t *is_free) ALWAYSINLINE;
static INLINE void	set_tiny_meta_header_in_use(const void *ptr, msize_t msize) ALWAYSINLINE;
static INLINE void	set_tiny_meta_header_in_use_1(const void *ptr) ALWAYSINLINE;
static INLINE void	set_tiny_meta_header_middle(const void *ptr) ALWAYSINLINE;
static INLINE void	set_tiny_meta_header_free(const void *ptr, msize_t msize) ALWAYSINLINE;
static INLINE boolean_t	tiny_meta_header_is_free(const void *ptr) ALWAYSINLINE;
static INLINE void	*tiny_previous_preceding_free(void *ptr, msize_t *prev_msize) ALWAYSINLINE;

static void		tiny_free_list_add_ptr(szone_t *szone, magazine_t *tiny_mag_ptr, void *ptr, msize_t msize);
static void		tiny_free_list_remove_ptr(szone_t *szone, magazine_t *tiny_mag_ptr, void *ptr, msize_t msize);
static INLINE region_t	tiny_region_for_ptr_no_lock(szone_t *szone, const void *ptr) ALWAYSINLINE;

static void		tiny_finalize_region(szone_t *szone, magazine_t *tiny_mag_ptr);
static int		tiny_free_detach_region(szone_t *szone, magazine_t *tiny_mag_ptr, region_t r);
static size_t		tiny_free_reattach_region(szone_t *szone, magazine_t *tiny_mag_ptr, region_t r);
static void		tiny_free_scan_madvise_free(szone_t *szone, magazine_t *depot_ptr, region_t r);
static region_t		tiny_free_try_depot_unmap_no_lock(szone_t *szone, magazine_t *depot_ptr, region_trailer_t *node);
static boolean_t	tiny_free_do_recirc_to_depot(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index);
static region_t		tiny_find_msize_region(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, msize_t msize);
static boolean_t	tiny_get_region_from_depot(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, msize_t msize);

static INLINE boolean_t	tiny_free_no_lock(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, region_t region,
										  void *ptr, msize_t msize) ALWAYSINLINE;
static void		*tiny_malloc_from_region_no_lock(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index,
												 msize_t msize, void *fresh_region);
static boolean_t	tiny_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size);
static boolean_t	tiny_check_region(szone_t *szone, region_t region);
static kern_return_t	tiny_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone,
											   memory_reader_t reader, vm_range_recorder_t recorder);
static void		*tiny_malloc_from_free_list(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index,
											msize_t msize);
static INLINE void	*tiny_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested) ALWAYSINLINE;
static INLINE void	free_tiny(szone_t *szone, void *ptr, region_t tiny_region, size_t known_size) ALWAYSINLINE;
static void		print_tiny_free_list(szone_t *szone);
static void		print_tiny_region(boolean_t verbose, region_t region, size_t bytes_at_start, size_t bytes_at_end);
static boolean_t	tiny_free_list_check(szone_t *szone, grain_t slot);

static INLINE void	small_meta_header_set_is_free(msize_t *meta_headers, unsigned index, msize_t msize) ALWAYSINLINE;
static INLINE void	small_meta_header_set_in_use(msize_t *meta_headers, msize_t index, msize_t msize) ALWAYSINLINE;
static INLINE void	small_meta_header_set_middle(msize_t *meta_headers, msize_t index) ALWAYSINLINE;
static void		small_free_list_add_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize);
static void		small_free_list_remove_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize);
static INLINE region_t	small_region_for_ptr_no_lock(szone_t *szone, const void *ptr) ALWAYSINLINE;

static void		small_finalize_region(szone_t *szone, magazine_t *small_mag_ptr);
static int		small_free_detach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r);
static size_t		small_free_reattach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r);
static void		small_free_scan_madvise_free(szone_t *szone, magazine_t *depot_ptr, region_t r);
static region_t		small_free_try_depot_unmap_no_lock(szone_t *szone, magazine_t *depot_ptr, region_trailer_t *node);
static boolean_t	small_free_do_recirc_to_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index);
static region_t		small_find_msize_region(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize);
static boolean_t	small_get_region_from_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize);
static INLINE boolean_t	small_free_no_lock(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, region_t region,
										   void *ptr, msize_t msize) ALWAYSINLINE;
static void		*small_malloc_from_region_no_lock(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index,
												  msize_t msize, void *fresh_region);
static boolean_t	small_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size);
static boolean_t	small_check_region(szone_t *szone, region_t region);
static kern_return_t	small_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone,
												memory_reader_t reader, vm_range_recorder_t recorder);
static void		*small_malloc_from_free_list(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index,
											 msize_t msize);
static INLINE void	*small_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested) ALWAYSINLINE;
static INLINE void	free_small(szone_t *szone, void *ptr, region_t small_region, size_t known_size) ALWAYSINLINE;
static void		print_small_free_list(szone_t *szone);
static void		print_small_region(szone_t *szone, boolean_t verbose, region_t region, size_t bytes_at_start, size_t bytes_at_end);
static boolean_t	small_free_list_check(szone_t *szone, grain_t grain);

#if DEBUG_MALLOC
static void		large_debug_print(szone_t *szone);
#endif
static large_entry_t	*large_entry_for_pointer_no_lock(szone_t *szone, const void *ptr);
static void		large_entry_insert_no_lock(szone_t *szone, large_entry_t range);
static INLINE void	large_entries_rehash_after_entry_no_lock(szone_t *szone, large_entry_t *entry) ALWAYSINLINE;
static INLINE large_entry_t *large_entries_alloc_no_lock(szone_t *szone, unsigned num) ALWAYSINLINE;
static void		large_entries_free_no_lock(szone_t *szone, large_entry_t *entries, unsigned num,
										   vm_range_t *range_to_deallocate);
static large_entry_t	*large_entries_grow_no_lock(szone_t *szone, vm_range_t *range_to_deallocate);
static vm_range_t	large_entry_free_no_lock(szone_t *szone, large_entry_t *entry);
static NOINLINE		kern_return_t	large_in_use_enumerator(task_t task, void *context,
															unsigned type_mask, vm_address_t large_entries_address,
															unsigned num_entries, memory_reader_t reader,
															vm_range_recorder_t recorder);
static void		*large_malloc(szone_t *szone, size_t num_kernel_pages, unsigned char alignment, boolean_t cleared_requested);
static NOINLINE void	free_large(szone_t *szone, void *ptr);
static INLINE int	large_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size) ALWAYSINLINE;

/*
 * Mark these NOINLINE to avoid bloating the purgeable zone call backs
 */
static NOINLINE void	szone_free(szone_t *szone, void *ptr);
static NOINLINE void	*szone_malloc_should_clear(szone_t *szone, size_t size, boolean_t cleared_requested);
static NOINLINE void	*szone_malloc(szone_t *szone, size_t size);
static NOINLINE void	*szone_calloc(szone_t *szone, size_t num_items, size_t size);
static NOINLINE void	*szone_valloc(szone_t *szone, size_t size);
static NOINLINE size_t	szone_size_try_large(szone_t *szone, const void *ptr);
static NOINLINE size_t	szone_size(szone_t *szone, const void *ptr);
static NOINLINE void	*szone_realloc(szone_t *szone, void *ptr, size_t new_size);
static NOINLINE void	*szone_memalign(szone_t *szone, size_t alignment, size_t size);
static NOINLINE void	szone_free_definite_size(szone_t *szone, void *ptr, size_t size);
static NOINLINE unsigned szone_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count);
static NOINLINE void	szone_batch_free(szone_t *szone, void **to_be_freed, unsigned count);
static void		szone_destroy(szone_t *szone);
static NOINLINE size_t	szone_good_size(szone_t *szone, size_t size);

static NOINLINE boolean_t szone_check_all(szone_t *szone, const char *function);
static boolean_t	szone_check(szone_t *szone);
static kern_return_t	szone_ptr_in_use_enumerator(task_t task, void *context,
													unsigned type_mask, vm_address_t zone_address,
													memory_reader_t reader, vm_range_recorder_t recorder);
static NOINLINE void	szone_print(szone_t *szone, boolean_t verbose);
static void		szone_log(malloc_zone_t *zone, void *log_address);
static void		szone_force_lock(szone_t *szone);
static INLINE void	szone_force_lock_magazine(szone_t *szone, magazine_t *mag);
static void		szone_force_unlock(szone_t *szone);
static boolean_t	szone_locked(szone_t *szone);

static void		szone_statistics(szone_t *szone, malloc_statistics_t *stats);

static void		purgeable_free(szone_t *szone, void *ptr);
static void		*purgeable_malloc(szone_t *szone, size_t size);
static void		*purgeable_calloc(szone_t *szone, size_t num_items, size_t size);
static void		*purgeable_valloc(szone_t *szone, size_t size);
static size_t		purgeable_size(szone_t *szone, const void *ptr);
static void		*purgeable_realloc(szone_t *szone, void *ptr, size_t new_size);
static void		*purgeable_memalign(szone_t *szone, size_t alignment, size_t size);
static void		purgeable_free_definite_size(szone_t *szone, void *ptr, size_t size);
static unsigned		purgeable_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count);
static void		purgeable_batch_free(szone_t *szone, void **to_be_freed, unsigned count);
static void		purgeable_destroy(szone_t *szone);
static size_t		purgeable_good_size(szone_t *szone, size_t size);

static boolean_t	purgeable_check(szone_t *szone);
static kern_return_t	purgeable_ptr_in_use_enumerator(task_t task, void *context,
														unsigned type_mask, vm_address_t zone_address,
														memory_reader_t reader, vm_range_recorder_t recorder);
static void		purgeable_print(szone_t *szone, boolean_t verbose);
static void		purgeable_log(malloc_zone_t *zone, void *log_address);
static void		purgeable_force_lock(szone_t *szone);
static void		purgeable_force_unlock(szone_t *szone);
static boolean_t	purgeable_locked(szone_t *szone);

static void		purgeable_statistics(szone_t *szone, malloc_statistics_t *stats);

static void		*frozen_malloc(szone_t *zone, size_t new_size);
static void		*frozen_calloc(szone_t *zone, size_t num_items, size_t size);
static void		*frozen_valloc(szone_t *zone, size_t new_size);
static void		*frozen_realloc(szone_t *zone, void *ptr, size_t new_size);
static void		frozen_free(szone_t *zone, void *ptr);
static void		frozen_destroy(szone_t *zone);

static volatile uintptr_t entropic_address = 0;
static volatile uintptr_t entropic_limit = 0;
#define ENTROPIC_KABILLION 0x10000000 /* 256Mb */

extern uint64_t malloc_entropy[2];

static inline void
SZONE_LOCK(szone_t *szone) {
	_malloc_lock_lock(&szone->large_szone_lock);
}

static inline void
SZONE_UNLOCK(szone_t *szone) {
	_malloc_lock_unlock(&szone->large_szone_lock);
}

static inline bool
SZONE_TRY_LOCK(szone_t *szone) {
	return _malloc_lock_trylock(&szone->large_szone_lock);
}

static inline void
SZONE_MAGAZINE_PTR_LOCK(szone_t *szone, magazine_t *mag_ptr) {
	_malloc_lock_lock(&mag_ptr->magazine_lock);
}

static inline void
SZONE_MAGAZINE_PTR_UNLOCK(szone_t *szone, magazine_t *mag_ptr) {
	_malloc_lock_unlock(&mag_ptr->magazine_lock);
}

static inline bool
SZONE_MAGAZINE_PTR_TRY_LOCK(szone_t *szone, magazine_t *mag_ptr) {
	return _malloc_lock_trylock(&mag_ptr->magazine_lock);
}

static inline void yield(void) {
	thread_switch(MACH_PORT_NULL, SWITCH_OPTION_DEPRESS, 1);
}

#if DEBUG_MALLOC
# define LOG(szone,ptr)							\
	(szone->log_address && (((uintptr_t)szone->log_address == -1) ||	\
	(szone->log_address == (void *)(ptr))))
#else
# define LOG(szone,ptr)		0
#endif

#if DEBUG_MALLOC || DEBUG_CLIENT
# define CHECK(szone,fun)						\
	if ((szone)->debug_flags & CHECK_REGIONS)				\
	szone_check_all(szone, fun)
#else
# define CHECK(szone,fun)						\
	do {} while (0)
#endif

/*********************	VERY LOW LEVEL UTILITIES  ************************/

static void
szone_sleep(void)
{
	if (getenv("MallocErrorStop")) {
		_malloc_printf(ASL_LEVEL_NOTICE, "*** sending SIGSTOP to help debug\n");
		kill(getpid(), SIGSTOP);
	} else if (getenv("MallocErrorSleep")) {
		_malloc_printf(ASL_LEVEL_NOTICE, "*** sleeping to help debug\n");
		sleep(3600); // to help debug
	}
}

// msg prints after fmt, ...
static NOINLINE void
szone_error(szone_t *szone, int is_corruption, const char *msg, const void *ptr, const char *fmt, ...)
{
	va_list ap;
	_SIMPLE_STRING b = _simple_salloc();

	if (b) {
		if (fmt) {
			va_start(ap, fmt);
			_simple_vsprintf(b, fmt, ap);
			va_end(ap);
		}
		if (ptr) {
			_simple_sprintf(b, "*** error for object %p: %s\n", ptr, msg);
		} else {
			_simple_sprintf(b, "*** error: %s\n", msg);
		}
		malloc_printf("%s*** set a breakpoint in malloc_error_break to debug\n", _simple_string(b));
	} else {
		/*
		 * Should only get here if vm_allocate() can't get a single page of
		 * memory, implying _simple_asl_log() would also fail.  So we just
		 * print to the file descriptor.
		 */
		if (fmt) {
			va_start(ap, fmt);
			_malloc_vprintf(MALLOC_PRINTF_NOLOG, fmt, ap);
			va_end(ap);
		}
		if (ptr) {
			_malloc_printf(MALLOC_PRINTF_NOLOG, "*** error for object %p: %s\n", ptr, msg);
		} else {
			_malloc_printf(MALLOC_PRINTF_NOLOG, "*** error: %s\n", msg);
		}
		_malloc_printf(MALLOC_PRINTF_NOLOG, "*** set a breakpoint in malloc_error_break to debug\n");
	}
	malloc_error_break();
#if DEBUG_MALLOC
	szone_print(szone, 1);
#endif
	szone_sleep();
	// Call abort() if this is a memory corruption error and the abort on
	// corruption flag is set, or if any error should abort.
	if ((is_corruption && (szone->debug_flags & SCALABLE_MALLOC_ABORT_ON_CORRUPTION)) ||
		(szone->debug_flags & SCALABLE_MALLOC_ABORT_ON_ERROR)) {
		CRSetCrashLogMessage(b ? _simple_string(b) : msg);
		abort();
	} else if (b) {
		_simple_sfree(b);
	}
}

static void
protect(void *address, size_t size, unsigned protection, unsigned debug_flags)
{
	kern_return_t	err;

	if (!(debug_flags & SCALABLE_MALLOC_DONT_PROTECT_PRELUDE)) {
		err = mprotect((void *)((uintptr_t)address - vm_page_quanta_size), vm_page_quanta_size, protection);
		if (err) {
			malloc_printf("*** can't protect(%p) region for prelude guard page at %p\n",
						  protection,(uintptr_t)address - vm_page_quanta_size);
		}
	}
	if (!(debug_flags & SCALABLE_MALLOC_DONT_PROTECT_POSTLUDE)) {
		err = mprotect((void *)(round_page_quanta(((uintptr_t)address + size))), vm_page_quanta_size, protection);
		if (err) {
			malloc_printf("*** can't protect(%p) region for postlude guard page at %p\n",
						  protection, (uintptr_t)address + size);
		}
	}
}

static void *
allocate_pages(szone_t *szone, size_t size, unsigned char align, unsigned debug_flags, int vm_page_label)
{
	boolean_t add_guard_pages = debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES;
	boolean_t purgeable = debug_flags & SCALABLE_MALLOC_PURGEABLE;
	mach_vm_address_t vm_addr;
	uintptr_t addr;
	mach_vm_size_t allocation_size = round_page_quanta(size);
	mach_vm_offset_t allocation_mask = ((mach_vm_offset_t)1 << align) - 1;
	int alloc_flags = VM_FLAGS_ANYWHERE | VM_MAKE_TAG(vm_page_label);
	kern_return_t kr;

	if (!allocation_size) allocation_size = vm_page_quanta_size;
	if (add_guard_pages) {
		if (align > vm_page_quanta_shift) {
			/* <rdar://problem/16601499> alignment greater than pagesize needs more work */
			allocation_size += (1<<align) + vm_page_quanta_size;
		} else {
			allocation_size += 2 * vm_page_quanta_size;
		}
	}

	if (purgeable) alloc_flags |= VM_FLAGS_PURGABLE;
	if (allocation_size < size) // size_t arithmetic wrapped!
		return NULL;

	vm_addr = vm_page_quanta_size;
	kr = mach_vm_map(mach_task_self(), &vm_addr, allocation_size,
			allocation_mask, alloc_flags, MEMORY_OBJECT_NULL, 0, FALSE,
			VM_PROT_DEFAULT, VM_PROT_ALL, VM_INHERIT_DEFAULT);
	if (kr) {
		szone_error(szone, 0, "can't allocate region", NULL,
				"*** mach_vm_map(size=%lu) failed (error code=%d)\n", size, kr);
		return NULL;
	}
	addr = (uintptr_t)vm_addr;

	if (add_guard_pages) {
		if (align > vm_page_quanta_shift) {
			/* <rdar://problem/16601499> calculate the first address inside the alignment padding
			 * where we can place the guard page and still be aligned.
			 *
			 * |-----------------------------------------------------------|
			 * |leading|gp|                  alloc                  |gp| t |
			 * |-----------------------------------------------------------|
			 */
			uintptr_t alignaddr = ((addr + vm_page_quanta_size) + (1<<align) - 1) & ~((1<<align) - 1);
			size_t leading = alignaddr - addr - vm_page_quanta_size;
			size_t trailing = (1<<align) - vm_page_quanta_size - leading;

			/* Unmap the excess area. */
			kr = mach_vm_deallocate(mach_task_self(), addr, leading);
			if (kr) {
				szone_error(szone, 0, "can't unmap excess guard region", NULL,
						"*** mach_vm_deallocate(addr=%p, size=%lu) failed (code=%d)", addr, leading, kr);
				return NULL;
			}

			kr = mach_vm_deallocate(mach_task_self(), addr + allocation_size - trailing, trailing);
			if (kr) {
				szone_error(szone, 0, "can't unmap excess trailing guard region", NULL,
						"*** mach_vm_deallocate(addr=%p, size=%lu) failed (code=%d)", addr + allocation_size - trailing, trailing, kr);
				return NULL;
			}

			addr = alignaddr;
		} else {
			addr += vm_page_quanta_size;
		}
		protect((void *)addr, size, PROT_NONE, debug_flags);
	}
	return (void *)addr;
}

static void *
allocate_pages_securely(szone_t *szone, size_t size, unsigned char align, int vm_page_label)
{
	mach_vm_address_t vm_addr;
	uintptr_t addr;
	mach_vm_size_t allocation_size = round_page_quanta(size);
	mach_vm_offset_t allocation_mask = ((mach_vm_offset_t)1 << align) - 1;
	int alloc_flags = VM_FLAGS_ANYWHERE | VM_MAKE_TAG(vm_page_label);
	kern_return_t kr;

	if (szone->debug_flags & DISABLE_ASLR) {
		return allocate_pages(szone, size, align, 0, vm_page_label);
	}

	if (!allocation_size) allocation_size = vm_page_quanta_size;
	if (allocation_size < size) // size_t arithmetic wrapped!
		return NULL;

retry:
	vm_addr = entropic_address;
	kr = mach_vm_map(mach_task_self(), &vm_addr, allocation_size,
			allocation_mask, alloc_flags, MEMORY_OBJECT_NULL, 0, FALSE,
			VM_PROT_DEFAULT, VM_PROT_ALL, VM_INHERIT_DEFAULT);
	if (kr == KERN_NO_SPACE) {
		vm_addr = vm_page_quanta_size;
		kr = mach_vm_map(mach_task_self(), &vm_addr, allocation_size,
				allocation_mask, alloc_flags, MEMORY_OBJECT_NULL, 0, FALSE,
				VM_PROT_DEFAULT, VM_PROT_ALL, VM_INHERIT_DEFAULT);
	}
	if (kr) {
		szone_error(szone, 0, "can't allocate region securely", NULL,
				"*** mach_vm_map(size=%lu) failed (error code=%d)\n", size, kr);
		return NULL;
	}
	addr = (uintptr_t)vm_addr;

	// Don't allow allocation to rise above entropic_limit (for tidiness).
	if (addr + allocation_size > entropic_limit) { // Exhausted current range?
		uintptr_t t = entropic_address;
		uintptr_t u = t - ENTROPIC_KABILLION;

		if (u < t) { // provided we don't wrap, deallocate and retry, in the expanded entropic range
			mach_vm_deallocate(mach_task_self(), vm_addr, allocation_size);
			(void)__sync_bool_compare_and_swap(&entropic_address, t, u); // Just one reduction please
			goto retry;
		}
		// fall through to use what we got
	}

	if (addr < entropic_address) { // we wrapped to find this allocation, expand the entropic range
		uintptr_t t = entropic_address;
		uintptr_t u = t - ENTROPIC_KABILLION;
		if (u < t)
			(void)__sync_bool_compare_and_swap(&entropic_address, t, u); // Just one reduction please
		// fall through to use what we got
	}
	return (void *)addr;
}

static void
deallocate_pages(szone_t *szone, void *addr, size_t size, unsigned debug_flags)
{
	boolean_t add_guard_pages = debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES;
	mach_vm_address_t vm_addr = (mach_vm_address_t)addr;
	mach_vm_size_t allocation_size = size;
	kern_return_t kr;

	if (add_guard_pages) {
		vm_addr -= vm_page_quanta_size;
		allocation_size += 2 * vm_page_quanta_size;
	}
	kr = mach_vm_deallocate(mach_task_self(), vm_addr, allocation_size);
	if (kr && szone)
		szone_error(szone, 0, "Can't deallocate_pages region", addr, NULL);
}

/* On OS X we use MADV_FREE_REUSABLE, which signals the kernel to remove the given
 * pages from the memory statistics for our process. However, on returning that memory
 * to use we have to signal that it has been reused.
 *
 * On iOS MADV_FREE is used, which does no such tinkering and madvise_reuse_range is a
 * no-op.
 */
#if TARGET_OS_EMBEDDED
# define MADVISE_STYLE MADV_FREE
#else
# define MADVISE_STYLE MADV_FREE_REUSABLE
#endif

static int
madvise_free_range(szone_t *szone, region_t r, uintptr_t pgLo, uintptr_t pgHi, uintptr_t *last)
{
	if (pgHi > pgLo) {
		size_t len = pgHi - pgLo;

		if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) {
			memset((void *)pgLo, SCRUBBLE_BYTE, len); // Scribble on MADV_FREEd memory
		}

#if TARGET_OS_EMBEDDED
		if (last) {
			if (*last == pgLo)
				return 0;

			*last = pgLo;
		}
#endif

		MAGMALLOC_MADVFREEREGION((void *)szone, (void *)r, (void *)pgLo, len); // DTrace USDT Probe
		if (-1 == madvise((void *)pgLo, len, MADVISE_STYLE)) {
			/* -1 return: VM map entry change makes this unfit for reuse. Something evil lurks. */
#if DEBUG_MADVISE
			szone_error(szone, 0, "madvise_free_range madvise(..., MADV_FREE_REUSABLE) failed",
						(void *)pgLo, "length=%d\n", len);
#endif
		}
	}
	return 0;
}

static int
madvise_reuse_range(szone_t *szone, region_t r, uintptr_t pgLo, uintptr_t phHi)
{
#if !TARGET_OS_EMBEDDED
	if (phHi > pgLo) {
		size_t len = phHi - pgLo;

		if (madvise((void *)pgLo, len, MADV_FREE_REUSE) == -1) {
			/* -1 return: VM map entry change makes this unfit for reuse. Something evil lurks. */
#if DEBUG_MADVISE
			szone_error(szone, 0, "madvise_reuse_range madvise(..., MADV_FREE_REUSE) failed",
					sparse_region, "length=%d\n", TINY_REGION_PAYLOAD_BYTES);
#endif
			return 1;
		}
	}
#endif
	return 0;
}

static kern_return_t
_szone_default_reader(task_t task, vm_address_t address, vm_size_t size, void **ptr)
{
	*ptr = (void *)address;
	return 0;
}

/*
 * These commpage routines provide fast access to the logical cpu number
 * of the calling processor assuming no pre-emption occurs.
 */

static INLINE mag_index_t
mag_get_thread_index(szone_t *szone)
{
	return _os_cpu_number() & (TINY_MAX_MAGAZINES - 1);
}

static magazine_t *
mag_lock_zine_for_region_trailer(szone_t *szone, magazine_t *magazines, region_trailer_t *trailer, mag_index_t mag_index)
{
	mag_index_t refreshed_index;
	magazine_t *mag_ptr = &(magazines[mag_index]);

	// Take the lock  on entry.
	SZONE_MAGAZINE_PTR_LOCK(szone, mag_ptr);

	// Now in the time it took to acquire the lock, the region may have migrated
	// from one magazine to another. In which case the magazine lock we obtained
	// (namely magazines[mag_index].mag_lock) is stale. If so, keep on tryin' ...
	while (mag_index != (refreshed_index = trailer->mag_index)) { // Note assignment

		SZONE_MAGAZINE_PTR_UNLOCK(szone, mag_ptr);

		mag_index = refreshed_index;
		mag_ptr = &(magazines[mag_index]);
		SZONE_MAGAZINE_PTR_LOCK(szone, mag_ptr);
	}

	return mag_ptr;
}

/*******************************************************************************
 * Region hash implementation
 *
 * This is essentially a duplicate of the existing Large allocator hash, minus
 * the ability to remove entries.  The two should be combined eventually.
 ******************************************************************************/
#pragma mark region hash

/*
 * hash_lookup_region_no_lock - Scan a hash ring looking for an entry for a
 * given region.
 *
 * FIXME: If consecutive queries of the same region are likely, a one-entry
 * cache would likely be a significant performance win here.
 */
static INLINE rgnhdl_t
hash_lookup_region_no_lock(region_t *regions, size_t num_entries, size_t shift, region_t r) {
	size_t	index, hash_index;
	rgnhdl_t	entry;

	if (!num_entries)
		return 0;

	// Multiplicative hash where the multiplier is a prime near (ULONG_MAX / phi). [phi = 1.618033...]
	// Since the values of (((uintptr_t)r >> HASH_BLOCKS_ALIGN) are (roughly) an ascending sequence of integers,
	// this hash works really well. See Knuth TAOCP, Vol. 3.
#if __LP64__
	index = hash_index = (((uintptr_t)r >> HASH_BLOCKS_ALIGN) * 11400714819323198549ULL) >> (64 - shift);
#else
	index = hash_index = (((uintptr_t)r >> HASH_BLOCKS_ALIGN) * 2654435761UL) >> (32 - shift);
#endif
	do {
		entry = regions + index;
		if (*entry == 0)
			return 0;
		if (*entry == r)
			return entry;
		if (++index == num_entries)
			index = 0;
	} while (index != hash_index);
	return 0;
}

/*
 * hash_region_insert_no_lock - Insert a region into the hash ring.
 */
static void
hash_region_insert_no_lock(region_t *regions, size_t num_entries, size_t shift, region_t r) {
	size_t	index, hash_index;
	rgnhdl_t	entry;

	// Multiplicative hash where the multiplier is a prime near (ULONG_MAX / phi). [phi = 1.618033...]
	// Since the values of (((uintptr_t)r >> HASH_BLOCKS_ALIGN) are (roughly) an ascending sequence of integers,
	// this hash works really well. See Knuth TAOCP, Vol. 3.
#if __LP64__
	index = hash_index = (((uintptr_t)r >> HASH_BLOCKS_ALIGN) * 11400714819323198549ULL) >> (64 - shift);
#else
	index = hash_index = (((uintptr_t)r >> HASH_BLOCKS_ALIGN) * 2654435761UL) >> (32 - shift);
#endif
	do {
		entry = regions + index;
		if (*entry == HASHRING_OPEN_ENTRY || *entry == HASHRING_REGION_DEALLOCATED) {
			*entry = r;
			return;
		}
		if (++index == num_entries)
			index = 0;
	} while (index != hash_index);
}

/*
 * hash_regions_alloc_no_lock - Allocate space for a number of entries.  This
 * must be a VM allocation as to avoid recursing between allocating a new small
 * region, and asking the small region to allocate space for the new list of
 * regions.
 */
static region_t *
hash_regions_alloc_no_lock(szone_t *szone, size_t num_entries)
{
	size_t	size = num_entries * sizeof(region_t);

	return allocate_pages(szone, round_page_quanta(size), 0, 0, VM_MEMORY_MALLOC);
}

/*
 * hash_regions_grow_no_lock - Grow the hash ring, and rehash the entries.
 * Return the new region and new size to update the szone.  Do not deallocate
 * the old entries since someone may still be allocating them.
 */
static region_t *
hash_regions_grow_no_lock(szone_t *szone, region_t *regions, size_t old_size, size_t *mutable_shift,
						  size_t *new_size)
{
	// double in size and allocate memory for the regions
	*new_size = old_size + old_size;
	*mutable_shift = *mutable_shift + 1;
	region_t *new_regions = hash_regions_alloc_no_lock(szone, *new_size);

	// rehash the entries into the new list
	size_t index;
	for (index = 0; index < old_size; ++index) {
		region_t r = regions[index];
		if (r != HASHRING_OPEN_ENTRY && r != HASHRING_REGION_DEALLOCATED)
			hash_region_insert_no_lock(new_regions, *new_size, *mutable_shift, r);
	}
	return new_regions;
}

/*********************	FREE LIST UTILITIES  ************************/

// A free list entry is comprised of a pair of pointers, previous and next.
// These are used to implement a doubly-linked list, which permits efficient
// extraction.
//
// Because the free list entries are previously freed objects, a misbehaved
// program may write to a pointer after it has called free() on that pointer,
// either by dereference or buffer overflow from an adjacent pointer. This write
// would then corrupt the free list's previous and next pointers, leading to a
// crash.  In order to detect this case, we take advantage of the fact that
// malloc'd pointers are known to be at least 16 byte aligned, and thus have
// at least 4 trailing zero bits.
//
// When an entry is added to the free list, a checksum of the previous and next
// pointers is calculated and written to the high four bits of the respective
// pointers.  Upon detection of an invalid checksum, an error is logged and NULL
// is returned.  Since all code which un-checksums pointers checks for a NULL
// return, a potentially crashing or malicious dereference is avoided at the
// cost of leaking the corrupted block, and any subsequent blocks on the free
// list of that size.

static NOINLINE void
free_list_checksum_botch(szone_t *szone, free_list_t *ptr)
{
	szone_error(szone, 1, "incorrect checksum for freed object "
				"- object was probably modified after being freed.", ptr, NULL);
}

static INLINE uintptr_t free_list_gen_checksum(uintptr_t ptr)
{
	uint8_t chk;

	chk  = (unsigned char)(ptr >>  0);
	chk += (unsigned char)(ptr >>  8);
	chk += (unsigned char)(ptr >> 16);
	chk += (unsigned char)(ptr >> 24);
#if  __LP64__
	chk += (unsigned char)(ptr >> 32);
	chk += (unsigned char)(ptr >> 40);
	chk += (unsigned char)(ptr >> 48);
	chk += (unsigned char)(ptr >> 56);
#endif

	return chk & (uintptr_t)0xF;
}

#define NYBBLE 4
#if  __LP64__
#define ANTI_NYBBLE (64 - NYBBLE)
#else
#define ANTI_NYBBLE (32 - NYBBLE)
#endif

static INLINE uintptr_t
free_list_checksum_ptr(szone_t *szone, void *ptr)
{
	uintptr_t p = (uintptr_t)ptr;
	return (p >> NYBBLE) | (free_list_gen_checksum(p ^ szone->cookie) << ANTI_NYBBLE); // compiles to rotate instruction
}

static INLINE void *
free_list_unchecksum_ptr(szone_t *szone, ptr_union *ptr)
{
	ptr_union p;
	uintptr_t t = ptr->u;

	t = (t << NYBBLE) | (t >> ANTI_NYBBLE); // compiles to rotate instruction
	p.u = t &  ~(uintptr_t)0xF;

	if ((t & (uintptr_t)0xF) != free_list_gen_checksum(p.u ^ szone->cookie))
	{
		free_list_checksum_botch(szone, (free_list_t *)ptr);
		return NULL;
	}
	return p.p;
}

#undef ANTI_NYBBLE
#undef NYBBLE

static unsigned
free_list_count(szone_t *szone, free_list_t *ptr)
{
	unsigned	count = 0;

	while (ptr) {
		count++;
		ptr = free_list_unchecksum_ptr(szone, &ptr->next);
	}
	return count;
}

static INLINE void
recirc_list_extract(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node)
{
	// excise node from list
	if (NULL == node->prev)
		mag_ptr->firstNode = node->next;
	else
		node->prev->next = node->next;

	if (NULL == node->next)
		mag_ptr->lastNode = node->prev;
	else
		node->next->prev = node->prev;

	mag_ptr->recirculation_entries--;
}

static INLINE void
recirc_list_splice_last(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node)
{
	if (NULL == mag_ptr->lastNode) {
		mag_ptr->firstNode = node;
		node->prev = NULL;
	} else {
		node->prev = mag_ptr->lastNode;
		mag_ptr->lastNode->next = node;
	}
	mag_ptr->lastNode = node;
	node->next = NULL;
	node->recirc_suitable = FALSE;
	mag_ptr->recirculation_entries++;
}

static INLINE void
recirc_list_splice_first(szone_t *szone, magazine_t *mag_ptr, region_trailer_t *node)
{
	if (NULL == mag_ptr->firstNode) {
		mag_ptr->lastNode = node;
		node->next = NULL;
	} else {
		node->next = mag_ptr->firstNode;
		mag_ptr->firstNode->prev = node;
	}
	mag_ptr->firstNode = node;
	node->prev = NULL;
	node->recirc_suitable = FALSE;
	mag_ptr->recirculation_entries++;
}

/* Macros used to manipulate the uint32_t quantity mag_bitmap. */

/* BITMAPV variants are used by tiny. */
#if defined(__LP64__)
// assert(NUM_SLOTS == 64) in which case (slot >> 5) is either 0 or 1
#define BITMAPV_SET(bitmap,slot) 	(bitmap[(slot) >> 5] |= 1 << ((slot) & 31))
#define BITMAPV_CLR(bitmap,slot) 	(bitmap[(slot) >> 5] &= ~ (1 << ((slot) & 31)))
#define BITMAPV_BIT(bitmap,slot)	((bitmap[(slot) >> 5] >> ((slot) & 31)) & 1)
#define BITMAPV_CTZ(bitmap)		(__builtin_ctzl(bitmap))
#else
// assert(NUM_SLOTS == 32) in which case (slot >> 5) is always 0, so code it that way
#define BITMAPV_SET(bitmap,slot) 	(bitmap[0] |= 1 << (slot))
#define BITMAPV_CLR(bitmap,slot)	(bitmap[0] &= ~ (1 << (slot)))
#define BITMAPV_BIT(bitmap,slot) 	((bitmap[0] >> (slot)) & 1)
#define BITMAPV_CTZ(bitmap)		(__builtin_ctz(bitmap))
#endif

/* BITMAPN is used by small. (slot >> 5) takes on values from 0 to 7. */
#define BITMAPN_SET(bitmap,slot) 	(bitmap[(slot) >> 5] |= 1 << ((slot) & 31))
#define BITMAPN_CLR(bitmap,slot) 	(bitmap[(slot) >> 5] &= ~ (1 << ((slot) & 31)))
#define BITMAPN_BIT(bitmap,slot)	((bitmap[(slot) >> 5] >> ((slot) & 31)) & 1)

/* returns bit # of least-significant one bit, starting at 0 (undefined if !bitmap) */
#define BITMAP32_CTZ(bitmap)		(__builtin_ctz(bitmap[0]))

/*********************	TINY FREE LIST UTILITIES	************************/

// We encode the meta-headers as follows:
// Each quantum has an associated set of 2 bits:
// block_header when 1 says this block is the beginning of a block
// in_use when 1 says this block is in use
// so a block in use of size 3 is 1-1 0-X 0-X
// for a free block TINY_FREE_SIZE(ptr) carries the size and the bits are 1-0 X-X X-X
// for a block middle the bits are 0-0

// We store the meta-header bit arrays by interleaving them 32 bits at a time.
// Initial 32 bits of block_header, followed by initial 32 bits of in_use, followed
// by next 32 bits of block_header, followed by next 32 bits of in_use, etc.
// This localizes memory references thereby reducing cache and TLB pressures.

static INLINE void
BITARRAY_SET(uint32_t *bits, msize_t index)
{
	// index >> 5 identifies the uint32_t to manipulate in the conceptually contiguous bits array
	// (index >> 5) << 1 identifies the uint32_t allowing for the actual interleaving
	bits[(index >> 5) << 1] |= (1 << (index & 31));
}

static INLINE void
BITARRAY_CLR(uint32_t *bits, msize_t index)
{
	bits[(index >> 5) << 1] &= ~(1 << (index & 31));
}

static INLINE boolean_t
BITARRAY_BIT(uint32_t *bits, msize_t index)
{
	return ((bits[(index >> 5) << 1]) >> (index & 31)) & 1;
}

#if 0
static INLINE void	bitarray_mclr(uint32_t *bits, unsigned start, unsigned end) ALWAYSINLINE;

static INLINE void
bitarray_mclr(uint32_t *bits, unsigned start, unsigned end)
{
	// start >> 5 identifies the uint32_t to manipulate in the conceptually contiguous bits array
	// (start >> 5) << 1 identifies the uint32_t allowing for the actual interleaving
	uint32_t	*addr = bits + ((start >> 5) << 1);

	uint32_t	span = end - start;
	start = start & 31;
	end = start + span;

	if (end > 31) {
		addr[0] &= (0xFFFFFFFFU >> (31 - start)) >> 1;
		addr[2] &= (0xFFFFFFFFU << (end - 32));
	} else {
		unsigned mask = (0xFFFFFFFFU >> (31 - start)) >> 1;
		mask |= (0xFFFFFFFFU << end);
		addr[0] &= mask;
	}
}
#endif

/*
 * Obtain the size of a free tiny block (in msize_t units).
 */
static msize_t
get_tiny_free_size(const void *ptr)
{
	void	*next_block = (void *)((uintptr_t)ptr + TINY_QUANTUM);
	void	*region_end = TINY_REGION_END(TINY_REGION_FOR_PTR(ptr));

	// check whether the next block is outside the tiny region or a block header
	// if so, then the size of this block is one, and there is no stored size.
	if (next_block < region_end)
	{
		uint32_t	*next_header = TINY_BLOCK_HEADER_FOR_PTR(next_block);
		msize_t		next_index  = TINY_INDEX_FOR_PTR(next_block);

		if (!BITARRAY_BIT(next_header, next_index))
			return TINY_FREE_SIZE(ptr);
	}
	return 1;
}

/*
 * Get the size of the previous free block, which is stored in the last two
 * bytes of the block.  If the previous block is not free, then the result is
 * undefined.
 */
static msize_t
get_tiny_previous_free_msize(const void *ptr)
{
	// check whether the previous block is in the tiny region and a block header
	// if so, then the size of the previous block is one, and there is no stored
	// size.
	if (ptr != TINY_REGION_FOR_PTR(ptr))
	{
		void		*prev_block = (void *)((uintptr_t)ptr - TINY_QUANTUM);
		uint32_t	*prev_header = TINY_BLOCK_HEADER_FOR_PTR(prev_block);
		msize_t		prev_index  = TINY_INDEX_FOR_PTR(prev_block);
		if (BITARRAY_BIT(prev_header, prev_index))
			return 1;
		return TINY_PREVIOUS_MSIZE(ptr);
	}
	// don't read possibly unmapped memory before the beginning of the region
	return 0;
}

static INLINE msize_t
get_tiny_meta_header(const void *ptr, boolean_t *is_free)
{
	// returns msize and is_free
	// may return 0 for the msize component (meaning 65536)
	uint32_t	*block_header;
	msize_t	index;

	block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	index = TINY_INDEX_FOR_PTR(ptr);

	msize_t midx = (index >> 5) << 1;
	uint32_t mask = 1 << (index & 31);
	*is_free = 0;
	if (0 == (block_header[midx] & mask)) // if (!BITARRAY_BIT(block_header, index))
		return 0;
	if (0 == (block_header[midx + 1] & mask)) { // if (!BITARRAY_BIT(in_use, index))
		*is_free = 1;
		return get_tiny_free_size(ptr);
	}

	// index >> 5 identifies the uint32_t to manipulate in the conceptually contiguous bits array
	// (index >> 5) << 1 identifies the uint32_t allowing for the actual interleaving
#if defined(__LP64__)
	// The return value, msize, is computed as the distance to the next 1 bit in block_header.
	// That's guaranteed to be somewhwere in the next 64 bits. And those bits could span three
	// uint32_t block_header elements. Collect the bits into a single uint64_t and measure up with ffsl.
	uint32_t	*addr = ((uint32_t *)block_header) + ((index >> 5) << 1);
	uint32_t	bitidx = index & 31;
	uint64_t	word_lo = addr[0];
	uint64_t	word_mid = addr[2];
	uint64_t	word_hi = addr[4];
	uint64_t	word_lomid = (word_lo >> bitidx) | (word_mid << (32 - bitidx));
	uint64_t	word = bitidx ? word_lomid | (word_hi << (64 - bitidx)) : word_lomid;
	uint32_t	result = __builtin_ffsl(word >> 1);
#else
	// The return value, msize, is computed as the distance to the next 1 bit in block_header.
	// That's guaranteed to be somwhwere in the next 32 bits. And those bits could span two
	// uint32_t block_header elements. Collect the bits into a single uint32_t and measure up with ffs.
	uint32_t	*addr = ((uint32_t *)block_header) + ((index >> 5) << 1);
	uint32_t	bitidx = index & 31;
	uint32_t	word = bitidx ? (addr[0] >> bitidx) | (addr[2] << (32 - bitidx)) : addr[0];
	uint32_t	result = __builtin_ffs(word >> 1);
#endif
	return result;
}

static INLINE void
set_tiny_meta_header_in_use(const void *ptr, msize_t msize)
{
	uint32_t	*block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	msize_t	index = TINY_INDEX_FOR_PTR(ptr);
	msize_t	clr_msize = msize - 1;
	msize_t	midx = (index >> 5) << 1;
	uint32_t	val = (1 << (index & 31));

#if DEBUG_MALLOC
	if (msize >= NUM_TINY_SLOTS)
		malloc_printf("set_tiny_meta_header_in_use() invariant broken %p %d\n", ptr, msize);
	if ((unsigned)index + (unsigned)msize > 0x10000)
		malloc_printf("set_tiny_meta_header_in_use() invariant broken (2) %p %d\n", ptr, msize);
#endif

	block_header[midx] |= val; // BITARRAY_SET(block_header, index);
	block_header[midx + 1] |= val; // BITARRAY_SET(in_use, index);

	// bitarray_mclr(block_header, index, end_bit);
	// bitarray_mclr(in_use, index, end_bit);

	index++;
	midx = (index >> 5) << 1;

	unsigned	start = index & 31;
	unsigned	end = start + clr_msize;

#if defined(__LP64__)
	if (end > 63) {
		unsigned mask0 = (0xFFFFFFFFU >> (31 - start)) >> 1;
		unsigned mask1 = (0xFFFFFFFFU << (end - 64));
		block_header[midx + 0] &= mask0; // clear header
		block_header[midx + 1] &= mask0; // clear in_use
		block_header[midx + 2] = 0; // clear header
		block_header[midx + 3] = 0; // clear in_use
		block_header[midx + 4] &= mask1; // clear header
		block_header[midx + 5] &= mask1; // clear in_use
	} else
#endif
		if (end > 31) {
			unsigned mask0 = (0xFFFFFFFFU >> (31 - start)) >> 1;
			unsigned mask1 = (0xFFFFFFFFU << (end - 32));
			block_header[midx + 0] &= mask0;
			block_header[midx + 1] &= mask0;
			block_header[midx + 2] &= mask1;
			block_header[midx + 3] &= mask1;
		} else {
			unsigned mask = (0xFFFFFFFFU >> (31 - start)) >> 1;
			mask |= (0xFFFFFFFFU << end);
			block_header[midx + 0] &= mask;
			block_header[midx + 1] &= mask;
		}

	// we set the block_header bit for the following block to reaffirm next block is a block
	index += clr_msize;
	midx = (index >> 5) << 1;
	val = (1 << (index & 31));
	block_header[midx] |= val; // BITARRAY_SET(block_header, (index+clr_msize));
#if DEBUG_MALLOC
	{
		boolean_t ff;
		msize_t	mf;

		mf = get_tiny_meta_header(ptr, &ff);
		if (msize != mf) {
			malloc_printf("setting header for tiny in_use %p : %d\n", ptr, msize);
			malloc_printf("reading header for tiny %p : %d %d\n", ptr, mf, ff);
		}
	}
#endif
}

static INLINE void
set_tiny_meta_header_in_use_1(const void *ptr) // As above with msize == 1
{
	uint32_t	*block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	msize_t	index = TINY_INDEX_FOR_PTR(ptr);
	msize_t	midx = (index >> 5) << 1;
	uint32_t	val = (1 << (index & 31));

	block_header[midx] |= val; // BITARRAY_SET(block_header, index);
	block_header[midx + 1] |= val; // BITARRAY_SET(in_use, index);

	index++;
	midx = (index >> 5) << 1;
	val = (1 << (index & 31));

	block_header[midx] |= val; // BITARRAY_SET(block_header, (index+clr_msize))
}

static INLINE void
set_tiny_meta_header_middle(const void *ptr)
{
	// indicates this block is in the middle of an in use block
	uint32_t	*block_header;
	uint32_t	*in_use;
	msize_t	index;

	block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	in_use = TINY_INUSE_FOR_HEADER(block_header);
	index = TINY_INDEX_FOR_PTR(ptr);

	BITARRAY_CLR(block_header, index);
	BITARRAY_CLR(in_use, index);
}

static INLINE void
set_tiny_meta_header_free(const void *ptr, msize_t msize)
{
	// !msize is acceptable and means 65536
	uint32_t	*block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	msize_t	index = TINY_INDEX_FOR_PTR(ptr);
	msize_t	midx = (index >> 5) << 1;
	uint32_t	val = (1 << (index & 31));

#if DEBUG_MALLOC
	if ((unsigned)index + (unsigned)msize > 0x10000) {
		malloc_printf("setting header for tiny free %p msize too large: %d\n", ptr, msize);
	}
#endif

	block_header[midx] |= val; // BITARRAY_SET(block_header, index);
	block_header[midx + 1] &= ~val; // BITARRAY_CLR(in_use, index);

	// mark the end of this block if msize is > 1.  For msize == 0, the whole
	// region is free, so there is no following block. For msize == 1, there is
	// no space to write the size on 64 bit systems.  The size for 1 quantum
	// blocks is computed from the metadata bitmaps.
	if (msize > 1) {
		void	*follower = FOLLOWING_TINY_PTR(ptr, msize);
		TINY_PREVIOUS_MSIZE(follower) = msize;
		TINY_FREE_SIZE(ptr) = msize;
	}
	if (msize == 0) {
		TINY_FREE_SIZE(ptr) = msize;
	}
#if DEBUG_MALLOC
	boolean_t	ff;
	msize_t	mf = get_tiny_meta_header(ptr, &ff);
	if ((msize != mf) || !ff) {
		malloc_printf("setting header for tiny free %p : %u\n", ptr, msize);
		malloc_printf("reading header for tiny %p : %u %u\n", ptr, mf, ff);
	}
#endif
}

static INLINE boolean_t
tiny_meta_header_is_free(const void *ptr)
{
	uint32_t	*block_header;
	uint32_t	*in_use;
	msize_t	index;

	block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	in_use = TINY_INUSE_FOR_HEADER(block_header);
	index = TINY_INDEX_FOR_PTR(ptr);
	if (!BITARRAY_BIT(block_header, index))
		return 0;
	return !BITARRAY_BIT(in_use, index);
}

static INLINE void *
tiny_previous_preceding_free(void *ptr, msize_t *prev_msize)
{
	// returns the previous block, assuming and verifying it's free
	uint32_t	*block_header;
	uint32_t	*in_use;
	msize_t	index;
	msize_t	previous_msize;
	msize_t	previous_index;
	void	*previous_ptr;

	block_header = TINY_BLOCK_HEADER_FOR_PTR(ptr);
	in_use = TINY_INUSE_FOR_HEADER(block_header);
	index = TINY_INDEX_FOR_PTR(ptr);

	if (!index)
		return NULL;
	if ((previous_msize = get_tiny_previous_free_msize(ptr)) > index)
		return NULL;

	previous_index = index - previous_msize;
	previous_ptr = (void *)((uintptr_t)TINY_REGION_FOR_PTR(ptr) + TINY_BYTES_FOR_MSIZE(previous_index));
	if (!BITARRAY_BIT(block_header, previous_index))
		return NULL;
	if (BITARRAY_BIT(in_use, previous_index))
		return NULL;
	if (get_tiny_free_size(previous_ptr) != previous_msize)
		return NULL;

	// conservative check did match true check
	*prev_msize = previous_msize;
	return previous_ptr;
}

/*
 * Adds an item to the proper free list, and also marks the meta-header of the
 * block properly.
 * Assumes szone has been locked
 */
static void
tiny_free_list_add_ptr(szone_t *szone, magazine_t *tiny_mag_ptr, void *ptr, msize_t msize)
{
	grain_t	slot = (!msize || (msize >= NUM_TINY_SLOTS)) ? NUM_TINY_SLOTS - 1 : msize - 1;
	free_list_t	*free_ptr = ptr;
	free_list_t	*free_head = tiny_mag_ptr->mag_free_list[slot];

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
	}
	if (((uintptr_t)ptr) & (TINY_QUANTUM - 1)) {
		szone_error(szone, 1, "tiny_free_list_add_ptr: Unaligned ptr", ptr, NULL);
	}
#endif
	set_tiny_meta_header_free(ptr, msize);
	if (free_head) {
#if DEBUG_MALLOC
		if (free_list_unchecksum_ptr(szone, &free_head->previous)) {
			szone_error(szone, 1, "tiny_free_list_add_ptr: Internal invariant broken (free_head->previous)", ptr,
						"ptr=%p slot=%d free_head=%p previous=%p\n", ptr, slot, (void *)free_head, free_head->previous.p);
		}
		if (! tiny_meta_header_is_free(free_head)) {
			szone_error(szone, 1, "tiny_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)", ptr,
						"ptr=%p slot=%d free_head=%p\n", ptr, slot, (void *)free_head);
		}
#endif
		free_head->previous.u = free_list_checksum_ptr(szone, free_ptr);
	} else {
		BITMAPV_SET(tiny_mag_ptr->mag_bitmap, slot);
	}
	free_ptr->previous.u = free_list_checksum_ptr(szone, NULL);
	free_ptr->next.u = free_list_checksum_ptr(szone, free_head);

	tiny_mag_ptr->mag_free_list[slot] = free_ptr;
}

/*
 * Removes the item pointed to by ptr in the proper free list.
 * Assumes szone has been locked
 */
static void
tiny_free_list_remove_ptr(szone_t *szone, magazine_t *tiny_mag_ptr, void *ptr, msize_t msize)
{
	grain_t	slot = (!msize || (msize >= NUM_TINY_SLOTS)) ? NUM_TINY_SLOTS - 1 : msize - 1;
	free_list_t	*free_ptr = ptr, *next, *previous;

	next = free_list_unchecksum_ptr(szone, &free_ptr->next);
	previous = free_list_unchecksum_ptr(szone, &free_ptr->previous);

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
	}
#endif
	if (!previous) {
		// The block to remove is the head of the free list
#if DEBUG_MALLOC
		if (tiny_mag_ptr->mag_free_list[slot] != ptr) {
			szone_error(szone, 1, "tiny_free_list_remove_ptr: Internal invariant broken (tiny_mag_ptr->mag_free_list[slot])", ptr,
						"ptr=%p slot=%d msize=%d tiny_mag_ptr->mag_free_list[slot]=%p\n",
						ptr, slot, msize, (void *)tiny_mag_ptr->mag_free_list[slot]);
			return;
		}
#endif
		tiny_mag_ptr->mag_free_list[slot] = next;
		if (!next) BITMAPV_CLR(tiny_mag_ptr->mag_bitmap, slot);
	} else {
		// We know free_ptr is already checksummed, so we don't need to do it
		// again.
		previous->next = free_ptr->next;
	}
	if (next) {
		// We know free_ptr is already checksummed, so we don't need to do it
		// again.
		next->previous = free_ptr->previous;
	}
}

/*
 * tiny_region_for_ptr_no_lock - Returns the tiny region containing the pointer,
 * or NULL if not found.
 */
static INLINE region_t
tiny_region_for_ptr_no_lock(szone_t *szone, const void *ptr)
{
	rgnhdl_t r = hash_lookup_region_no_lock(szone->tiny_region_generation->hashed_regions,
											szone->tiny_region_generation->num_regions_allocated,
											szone->tiny_region_generation->num_regions_allocated_shift,
											TINY_REGION_FOR_PTR(ptr));
	return r ? *r : r;
}

static void
tiny_finalize_region(szone_t *szone, magazine_t *tiny_mag_ptr) {
	void      *last_block, *previous_block;
	uint32_t  *last_header;
	msize_t   last_msize, previous_msize, last_index;

	// It is possible that the block prior to the last block in the region has
	// been free'd, but was not coalesced with the free bytes at the end of the
	// block, since we treat the bytes at the end of the region as "in use" in
	// the meta headers. Attempt to coalesce the last block with the previous
	// block, so we don't violate the "no consecutive free blocks" invariant.
	//
	// FIXME: Need to investigate how much work would be required to increase
	//        'mag_bytes_free_at_end' when freeing the preceding block, rather
	//        than performing this workaround.
	//

	if (tiny_mag_ptr->mag_bytes_free_at_end) {
		last_block = (void *)
		((uintptr_t)TINY_REGION_END(tiny_mag_ptr->mag_last_region) - tiny_mag_ptr->mag_bytes_free_at_end);
		last_msize = TINY_MSIZE_FOR_BYTES(tiny_mag_ptr->mag_bytes_free_at_end);
		last_header = TINY_BLOCK_HEADER_FOR_PTR(last_block);
		last_index  = TINY_INDEX_FOR_PTR(last_block);

		// Before anything we transform any remaining mag_bytes_free_at_end into a
		// regular free block.  We take special care here to update the bitfield
		// information, since we are bypassing the normal free codepath.  If there
		// is more than one quanta worth of memory in mag_bytes_free_at_end, then
		// there will be two block headers:
		// 1) header for the free space at end, msize = 1
		// 2) header inserted by set_tiny_meta_header_in_use after block
		// We must clear the second one so that when the free block's size is
		// queried, we do not think the block is only 1 quantum in size because
		// of the second set header bit.
		if (last_index != (NUM_TINY_BLOCKS - 1))
			BITARRAY_CLR(last_header, (last_index + 1));

		previous_block = tiny_previous_preceding_free(last_block, &previous_msize);
		if (previous_block) {
			set_tiny_meta_header_middle(last_block);
			tiny_free_list_remove_ptr(szone, tiny_mag_ptr, previous_block, previous_msize);
			last_block = previous_block;
			last_msize += previous_msize;
		}

		// splice last_block into the free list
		tiny_free_list_add_ptr(szone, tiny_mag_ptr, last_block, last_msize);
		tiny_mag_ptr->mag_bytes_free_at_end = 0;
	}

#if ASLR_INTERNAL
	// Coalesce the big free block at start with any following free blocks
	if (tiny_mag_ptr->mag_bytes_free_at_start) {
		last_block = TINY_REGION_ADDRESS(tiny_mag_ptr->mag_last_region);
		last_msize = TINY_MSIZE_FOR_BYTES(tiny_mag_ptr->mag_bytes_free_at_start);

		void *next_block = (void *) ((uintptr_t)last_block + tiny_mag_ptr->mag_bytes_free_at_start);

		// clear the in use bit we were using to mark the end of the big start block
		set_tiny_meta_header_middle((void *)((uintptr_t)next_block - TINY_QUANTUM));

		// Coalesce the big start block with any following free blocks
		if (tiny_meta_header_is_free(next_block)) {
			msize_t next_msize = get_tiny_free_size(next_block);
			set_tiny_meta_header_middle(next_block);
			tiny_free_list_remove_ptr(szone, tiny_mag_ptr, next_block, next_msize);
			last_msize += next_msize;
		}

		// splice last_block into the free list
		tiny_free_list_add_ptr(szone, tiny_mag_ptr, last_block, last_msize);
		tiny_mag_ptr->mag_bytes_free_at_start = 0;
	}
#endif

	tiny_mag_ptr->mag_last_region = NULL;
}

static int
tiny_free_detach_region(szone_t *szone, magazine_t *tiny_mag_ptr, region_t r) {
	uintptr_t	start = (uintptr_t)TINY_REGION_ADDRESS(r);
	uintptr_t	current = start;
	uintptr_t	limit =  (uintptr_t)TINY_REGION_END(r);
	boolean_t	is_free;
	msize_t	msize;
	int		total_alloc = 0;

	while (current < limit) {
		msize = get_tiny_meta_header((void *)current, &is_free);
		if (is_free && !msize && (current == start)) {
			// first block is all free
			break;
		}
		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** tiny_free_detach_region error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			tiny_free_list_remove_ptr(szone, tiny_mag_ptr, (void *)current, msize);
		} else {
			total_alloc++;
		}
		current += TINY_BYTES_FOR_MSIZE(msize);
	}
	return total_alloc;
}

static size_t
tiny_free_reattach_region(szone_t *szone, magazine_t *tiny_mag_ptr, region_t r) {
	uintptr_t	start = (uintptr_t)TINY_REGION_ADDRESS(r);
	uintptr_t	current = start;
	uintptr_t	limit =  (uintptr_t)TINY_REGION_END(r);
	boolean_t	is_free;
	msize_t	msize;
	size_t	total_alloc = 0;

	while (current < limit) {
		msize = get_tiny_meta_header((void *)current, &is_free);
		if (is_free && !msize && (current == start)) {
			// first block is all free
			break;
		}
		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** tiny_free_reattach_region error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			tiny_free_list_add_ptr(szone, tiny_mag_ptr, (void *)current, msize);
		} else {
			total_alloc += TINY_BYTES_FOR_MSIZE(msize);
		}
		current += TINY_BYTES_FOR_MSIZE(msize);
	}
	return total_alloc;
}

typedef struct {
	uint8_t pnum, size;
} tiny_pg_pair_t;

static void NOINLINE /* want private stack frame for automatic array */
tiny_free_scan_madvise_free(szone_t *szone, magazine_t *depot_ptr, region_t r) {
	uintptr_t	start = (uintptr_t)TINY_REGION_ADDRESS(r);
	uintptr_t	current = start;
	uintptr_t	limit =  (uintptr_t)TINY_REGION_END(r);
	boolean_t	is_free;
	msize_t	msize;
	tiny_pg_pair_t advisory[((TINY_REGION_PAYLOAD_BYTES + vm_page_quanta_size - 1) >> vm_page_quanta_shift) >> 1]; // 256bytes stack allocated
	int		advisories = 0;

	// Scan the metadata identifying blocks which span one or more pages. Mark the pages MADV_FREE taking care to preserve free list
	// management data.
	while (current < limit) {
		msize = get_tiny_meta_header((void *)current, &is_free);
		if (is_free && !msize && (current == start)) {
			// first block is all free
#if DEBUG_MALLOC
			malloc_printf("*** tiny_free_scan_madvise_free first block is all free! %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			uintptr_t pgLo = round_page_quanta(start + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(start + TINY_REGION_SIZE - sizeof(msize_t));

			if (pgLo < pgHi) {
				advisory[advisories].pnum = (pgLo - start) >> vm_page_quanta_shift;
				advisory[advisories].size = (pgHi - pgLo) >> vm_page_quanta_shift;
				advisories++;
			}
			break;
		}
		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** tiny_free_scan_madvise_free error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			uintptr_t pgLo = round_page_quanta(current + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(current + TINY_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));

			if (pgLo < pgHi) {
				advisory[advisories].pnum = (pgLo - start) >> vm_page_quanta_shift;
				advisory[advisories].size = (pgHi - pgLo) >> vm_page_quanta_shift;
				advisories++;
			}
		}
		current += TINY_BYTES_FOR_MSIZE(msize);
	}

	if (advisories > 0) {
		int i;

		// So long as the following hold for this region:
		// (1) No malloc()'s are ever performed from the depot (hence free pages remain free,)
		// (2) The region is not handed over to a per-CPU magazine (where malloc()'s could be performed),
		// (3) The entire region is not mumap()'d (so the madvise's are applied to the intended addresses),
		// then the madvise opportunities collected just above can be applied outside all locks.
		// (1) is ensured by design, (2) and (3) are ensured by bumping the globally visible counter node->pinned_to_depot.

		OSAtomicIncrement32Barrier(&(REGION_TRAILER_FOR_TINY_REGION(r)->pinned_to_depot));
		SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
		for (i = 0; i < advisories; ++i) {
			uintptr_t addr = (advisory[i].pnum << vm_page_quanta_shift) + start;
			size_t size = advisory[i].size << vm_page_quanta_shift;

			madvise_free_range(szone, r, addr, addr + size, NULL);
		}
		SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
		OSAtomicDecrement32Barrier(&(REGION_TRAILER_FOR_TINY_REGION(r)->pinned_to_depot));
	}
}

static region_t
tiny_free_try_depot_unmap_no_lock(szone_t *szone, magazine_t *depot_ptr, region_trailer_t *node)
{
	if (0 < node->bytes_used ||
		0 < node->pinned_to_depot ||
		depot_ptr->recirculation_entries < (szone->num_tiny_magazines * 2)) {
		return NULL;
	}

	// disconnect node from Depot
	recirc_list_extract(szone, depot_ptr, node);

	// Iterate the region pulling its free entries off the (locked) Depot's free list
	region_t sparse_region = TINY_REGION_FOR_PTR(node);
	int objects_in_use = tiny_free_detach_region(szone, depot_ptr, sparse_region);

	if (0 == objects_in_use) {
		// Invalidate the hash table entry for this region with HASHRING_REGION_DEALLOCATED.
		// Using HASHRING_REGION_DEALLOCATED preserves the collision chain, using HASHRING_OPEN_ENTRY (0) would not.
		rgnhdl_t pSlot = hash_lookup_region_no_lock(szone->tiny_region_generation->hashed_regions,
													szone->tiny_region_generation->num_regions_allocated,
													szone->tiny_region_generation->num_regions_allocated_shift, sparse_region);
		if (NULL == pSlot) {
			szone_error(szone, 1, "tiny_free_try_depot_unmap_no_lock hash lookup failed:", NULL, "%p\n", sparse_region);
			return NULL;
		}
		*pSlot = HASHRING_REGION_DEALLOCATED;
		depot_ptr->num_bytes_in_magazine -= TINY_REGION_PAYLOAD_BYTES;
		__sync_fetch_and_add( &(szone->num_tiny_regions_dealloc), 1); // Atomically increment num_tiny_regions_dealloc

		// Caller will transfer ownership of the region back to the OS with no locks held
		MAGMALLOC_DEALLOCREGION((void *)szone, (void *)sparse_region, TINY_REGION_SIZE); // DTrace USDT Probe
		return sparse_region;
	} else {
		szone_error(szone, 1, "tiny_free_try_depot_unmap_no_lock objects_in_use not zero:", NULL, "%d\n", objects_in_use);
		return NULL;
	}
}

static boolean_t
tiny_free_do_recirc_to_depot(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index)
{
	// The entire magazine crossed the "emptiness threshold". Transfer a region
	// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
	// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.
	region_trailer_t *node = tiny_mag_ptr->firstNode;

	while (node && !node->recirc_suitable) {
		node = node->next;
	}

	if (NULL == node) {
#if DEBUG_MALLOC
		malloc_printf("*** tiny_free_do_recirc_to_depot end of list\n");
#endif
		return TRUE; // Caller must SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
	}

	region_t sparse_region = TINY_REGION_FOR_PTR(node);

	// Deal with unclaimed memory -- mag_bytes_free_at_end or mag_bytes_free_at_start
	if (sparse_region == tiny_mag_ptr->mag_last_region && (tiny_mag_ptr->mag_bytes_free_at_end || tiny_mag_ptr->mag_bytes_free_at_start)) {
		tiny_finalize_region(szone, tiny_mag_ptr);
	}

	// disconnect "suitable" node from magazine
	recirc_list_extract(szone, tiny_mag_ptr, node);

	// Iterate the region pulling its free entries off its (locked) magazine's free list
	int objects_in_use = tiny_free_detach_region(szone, tiny_mag_ptr, sparse_region);
	magazine_t *depot_ptr = &(szone->tiny_magazines[DEPOT_MAGAZINE_INDEX]);

	// hand over the region to the (locked) Depot
	SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);
	// this will cause tiny_free_list_add_ptr called by tiny_free_reattach_region to use
	// the depot as its target magazine, rather than magazine formerly associated with sparse_region
	MAGAZINE_INDEX_FOR_TINY_REGION(sparse_region) = DEPOT_MAGAZINE_INDEX;
	node->pinned_to_depot = 0;

	// Iterate the region putting its free entries on Depot's free list
	size_t bytes_inplay = tiny_free_reattach_region(szone, depot_ptr, sparse_region);

	tiny_mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
	tiny_mag_ptr->num_bytes_in_magazine -= TINY_REGION_PAYLOAD_BYTES;
	tiny_mag_ptr->mag_num_objects -= objects_in_use;

	SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr); // Unlock the originating magazine

	depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
	depot_ptr->num_bytes_in_magazine += TINY_REGION_PAYLOAD_BYTES;
	depot_ptr->mag_num_objects += objects_in_use;

	// connect to Depot as last node
	recirc_list_splice_last(szone, depot_ptr, node);

	MAGMALLOC_RECIRCREGION((void *)szone, (int)mag_index, (void *)sparse_region, TINY_REGION_SIZE,
						   (int)BYTES_USED_FOR_TINY_REGION(sparse_region));  // DTrace USDT Probe

	// Mark free'd dirty pages with MADV_FREE to reduce memory pressure
	tiny_free_scan_madvise_free(szone, depot_ptr, sparse_region);

	// If the region is entirely empty vm_deallocate() it outside the depot lock
	region_t r_dealloc = tiny_free_try_depot_unmap_no_lock(szone, depot_ptr, node);
	SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
	if (r_dealloc)
		deallocate_pages(szone, r_dealloc, TINY_REGION_SIZE, 0);
	return FALSE; // Caller need not unlock the originating magazine
}

static region_t
tiny_find_msize_region(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	free_list_t		*ptr;
	grain_t		slot = msize - 1;
	free_list_t		**free_list = tiny_mag_ptr->mag_free_list;
	free_list_t		**the_slot = free_list + slot;
	free_list_t		**limit;
#if defined(__LP64__)
	uint64_t		bitmap;
#else
	uint32_t		bitmap;
#endif
	// Assumes we've locked the magazine
	CHECK_MAGAZINE_PTR_LOCKED(szone, tiny_mag_ptr, __PRETTY_FUNCTION__);

	// Look for an exact match by checking the freelist for this msize.
	ptr = *the_slot;
	if (ptr)
		return TINY_REGION_FOR_PTR(ptr);

	// Mask off the bits representing slots holding free blocks smaller than the
	// size we need.  If there are no larger free blocks, try allocating from
	// the free space at the end of the tiny region.
#if defined(__LP64__)
	bitmap = ((uint64_t *)(tiny_mag_ptr->mag_bitmap))[0] & ~ ((1ULL << slot) - 1);
#else
	bitmap = tiny_mag_ptr->mag_bitmap[0] & ~ ((1 << slot) - 1);
#endif
	if (!bitmap)
		return NULL;

	slot = BITMAPV_CTZ(bitmap);
	limit = free_list + NUM_TINY_SLOTS - 1;
	free_list += slot;

	if (free_list < limit) {
		ptr = *free_list;
		if (ptr)
			return TINY_REGION_FOR_PTR(ptr);
		else {
			/* Shouldn't happen. Fall through to look at last slot. */
#if DEBUG_MALLOC
			malloc_printf("in tiny_find_msize_region(), mag_bitmap out of sync, slot=%d\n",slot);
#endif
		}
	}

	// We are now looking at the last slot, which contains blocks equal to, or
	// due to coalescing of free blocks, larger than (NUM_TINY_SLOTS - 1) * tiny quantum size.
	ptr = *limit;
	if (ptr)
		return TINY_REGION_FOR_PTR(ptr);

	return NULL;
}

static boolean_t
tiny_get_region_from_depot(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	magazine_t *depot_ptr = &(szone->tiny_magazines[DEPOT_MAGAZINE_INDEX]);

	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
	if (szone->num_tiny_magazines == 1) // Uniprocessor, single magazine, so no recirculation necessary
		return 0;

#if DEBUG_MALLOC
	if (DEPOT_MAGAZINE_INDEX == mag_index) {
		szone_error(szone, 1, "tiny_get_region_from_depot called for magazine index -1", NULL, NULL);
		return 0;
	}
#endif

	SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);

	// Appropriate a Depot'd region that can satisfy requested msize.
	region_trailer_t *node;
	region_t sparse_region;

	while (1) {
		sparse_region = tiny_find_msize_region(szone, depot_ptr, DEPOT_MAGAZINE_INDEX, msize);
		if (NULL == sparse_region) { // Depot empty?
			SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
			return 0;
		}

		node = REGION_TRAILER_FOR_TINY_REGION(sparse_region);
		if (0 >= node->pinned_to_depot)
			break;

		SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
		yield();
		SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);
	}

	// disconnect node from Depot
	recirc_list_extract(szone, depot_ptr, node);

	// Iterate the region pulling its free entries off the (locked) Depot's free list
	int objects_in_use = tiny_free_detach_region(szone, depot_ptr, sparse_region);

	// Transfer ownership of the region
	MAGAZINE_INDEX_FOR_TINY_REGION(sparse_region) = mag_index;
	node->pinned_to_depot = 0;

	// Iterate the region putting its free entries on its new (locked) magazine's free list
	size_t bytes_inplay = tiny_free_reattach_region(szone, tiny_mag_ptr, sparse_region);

	depot_ptr->mag_num_bytes_in_objects -= bytes_inplay;
	depot_ptr->num_bytes_in_magazine -= TINY_REGION_PAYLOAD_BYTES;
	depot_ptr->mag_num_objects -= objects_in_use;

	tiny_mag_ptr->mag_num_bytes_in_objects += bytes_inplay;
	tiny_mag_ptr->num_bytes_in_magazine += TINY_REGION_PAYLOAD_BYTES;
	tiny_mag_ptr->mag_num_objects += objects_in_use;

	// connect to magazine as first node
	recirc_list_splice_first(szone, tiny_mag_ptr, node);

	SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);

	// madvise() outside the Depot lock
	(void)madvise_reuse_range(szone, sparse_region, sparse_region, sparse_region+TINY_REGION_PAYLOAD_BYTES);

	MAGMALLOC_DEPOTREGION((void *)szone, (int)mag_index, (void *)sparse_region, TINY_REGION_SIZE,
						  (int)BYTES_USED_FOR_TINY_REGION(sparse_region)); // DTrace USDT Probe

	return 1;
}

#define K 1.5 // headroom measured in number of 1Mb regions
#define DENSITY_THRESHOLD(a) \
	((a) - ((a) >> 2)) // "Emptiness" f = 0.25, so "Density" is (1 - f)*a. Generally: ((a) - ((a) >> -log2(f)))

static INLINE boolean_t
tiny_free_no_lock(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, region_t region, void *ptr,
				  msize_t msize)
{
	void	*original_ptr = ptr;
	size_t	original_size = TINY_BYTES_FOR_MSIZE(msize);
	void	*next_block = ((unsigned char *)ptr + original_size);
	msize_t	previous_msize, next_msize;
	void	*previous;
	free_list_t	*big_free_block;
	free_list_t	*after_next_block;
	free_list_t	*before_next_block;

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in tiny_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
	}
	if (!msize) {
		szone_error(szone, 1, "trying to free tiny block that is too small", ptr,
					"in tiny_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
	}
#endif

	// We try to coalesce this block with the preceeding one
	previous = tiny_previous_preceding_free(ptr, &previous_msize);
	if (previous) {
#if DEBUG_MALLOC
		if (LOG(szone, ptr) || LOG(szone,previous)) {
			malloc_printf("in tiny_free_no_lock(), coalesced backwards for %p previous=%p\n", ptr, previous);
		}
#endif

		// clear the meta_header since this is no longer the start of a block
		set_tiny_meta_header_middle(ptr);
		tiny_free_list_remove_ptr(szone, tiny_mag_ptr, previous, previous_msize);
		ptr = previous;
		msize += previous_msize;
	}
	// We try to coalesce with the next block
	if ((next_block < TINY_REGION_END(region)) && tiny_meta_header_is_free(next_block)) {
		next_msize = get_tiny_free_size(next_block);
#if DEBUG_MALLOC
		if (LOG(szone, ptr) || LOG(szone, next_block)) {
			malloc_printf("in tiny_free_no_lock(), for ptr=%p, msize=%d coalesced forward=%p next_msize=%d\n",
						  ptr, msize, next_block, next_msize);
		}
#endif
		// If we are coalescing with the next block, and the next block is in
		// the last slot of the free list, then we optimize this case here to
		// avoid removing next_block from the slot (NUM_TINY_SLOTS - 1) and then adding ptr back
		// to slot (NUM_TINY_SLOTS - 1).
		if (next_msize >= NUM_TINY_SLOTS) {
			msize += next_msize;

			big_free_block = (free_list_t *)next_block;
			after_next_block = free_list_unchecksum_ptr(szone, &big_free_block->next);
			before_next_block = free_list_unchecksum_ptr(szone, &big_free_block->previous);

			if (!before_next_block) {
				tiny_mag_ptr->mag_free_list[NUM_TINY_SLOTS-1] = ptr;
			} else {
				before_next_block->next.u = free_list_checksum_ptr(szone, ptr);
			}

			if (after_next_block) {
				after_next_block->previous.u = free_list_checksum_ptr(szone, ptr);
			}

			// we don't need to checksum these since they are already checksummed
			((free_list_t *)ptr)->previous = big_free_block->previous;
			((free_list_t *)ptr)->next = big_free_block->next;

			// clear the meta_header to enable coalescing backwards
			set_tiny_meta_header_middle(big_free_block);
			set_tiny_meta_header_free(ptr, msize);

			goto tiny_free_ending;
		}
		tiny_free_list_remove_ptr(szone, tiny_mag_ptr, next_block, next_msize);
		set_tiny_meta_header_middle(next_block); // clear the meta_header to enable coalescing backwards
		msize += next_msize;
	}

	// The tiny cache already scribbles free blocks as they go through the
	// cache whenever msize < TINY_QUANTUM , so we do not need to do it here.
	if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && msize && (msize >= TINY_QUANTUM))
		memset(ptr, SCRABBLE_BYTE, TINY_BYTES_FOR_MSIZE(msize));

	tiny_free_list_add_ptr(szone, tiny_mag_ptr, ptr, msize);

tiny_free_ending:

	tiny_mag_ptr->mag_num_objects--;
	// we use original_size and not msize to avoid double counting the coalesced blocks
	tiny_mag_ptr->mag_num_bytes_in_objects -= original_size;

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_TINY_REGION(region);
	size_t bytes_used = node->bytes_used - original_size;
	node->bytes_used = bytes_used;

#if !TARGET_OS_EMBEDDED // Always madvise for embedded platforms
	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
	if (szone->num_tiny_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
		/* NOTHING */
	} else if (DEPOT_MAGAZINE_INDEX != mag_index) {
		// Emptiness discriminant
		if (bytes_used < DENSITY_THRESHOLD(TINY_REGION_PAYLOAD_BYTES)) {
			/* Region has crossed threshold from density to sparsity. Mark it "suitable" on the
			 recirculation candidates list. */
			node->recirc_suitable = TRUE;
		} else {
			/* After this free, we've found the region is still dense, so it must have been even more so before
			 the free. That implies the region is already correctly marked. Do nothing. */
		}

		// Has the entire magazine crossed the "emptiness threshold"? If so, transfer a region
		// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
		// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.
		size_t a = tiny_mag_ptr->num_bytes_in_magazine; // Total bytes allocated to this magazine
		size_t u = tiny_mag_ptr->mag_num_bytes_in_objects; // In use (malloc'd) from this magaqzine

		if (a - u > ((3 * TINY_REGION_PAYLOAD_BYTES) / 2) && u < DENSITY_THRESHOLD(a)) {
			return tiny_free_do_recirc_to_depot(szone, tiny_mag_ptr, mag_index);
		}

	} else {
#endif
		// Freed to Depot. N.B. Lock on tiny_magazines[DEPOT_MAGAZINE_INDEX] is already held
		// Calcuate the first page in the coalesced block that would be safe to mark MADV_FREE
		size_t free_header_size = sizeof(free_list_t) + sizeof(msize_t);
		uintptr_t safe_ptr = (uintptr_t)ptr + free_header_size;
		uintptr_t round_safe = round_page_quanta(safe_ptr);

		// Calcuate the last page in the coalesced block that would be safe to mark MADV_FREE
		size_t free_tail_size = sizeof(msize_t);
		uintptr_t safe_extent = (uintptr_t)ptr + TINY_BYTES_FOR_MSIZE(msize) - free_tail_size;
		uintptr_t trunc_extent = trunc_page_quanta(safe_extent);

		// The newly freed block may complete a span of bytes that cover a page. Mark it with MADV_FREE.
		if (round_safe < trunc_extent) { // Coalesced area covers a page (perhaps many)
			// Extend the freed block by the free region header and tail sizes to include pages
			// we may have coalesced that no longer host free region tails and headers.
			// This may extend over in-use ranges, but the MIN/MAX clamping below will fix that up.
			uintptr_t lo = trunc_page_quanta((uintptr_t)original_ptr - free_tail_size);
			uintptr_t hi = round_page_quanta((uintptr_t)original_ptr + original_size + free_header_size);

			uintptr_t free_lo = MAX(round_safe, lo);
			uintptr_t free_hi = MIN(trunc_extent, hi);

			if (free_lo < free_hi) {
				tiny_free_list_remove_ptr(szone, tiny_mag_ptr, ptr, msize);
				set_tiny_meta_header_in_use(ptr, msize);

				OSAtomicIncrement32Barrier(&(node->pinned_to_depot));
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				madvise_free_range(szone, region, free_lo, free_hi, &szone->last_tiny_advise);
				SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);
				OSAtomicDecrement32Barrier(&(node->pinned_to_depot));

				set_tiny_meta_header_free(ptr, msize);
				tiny_free_list_add_ptr(szone, tiny_mag_ptr, ptr, msize);
			}
		}

#if !TARGET_OS_EMBEDDED
		if (0 < bytes_used || 0 < node->pinned_to_depot) {
			/* Depot'd region is still live. Leave it in place on the Depot's recirculation list
			 so as to avoid thrashing between the Depot's free list and a magazines's free list
			 with detach_region/reattach_region */
		} else {
			/* Depot'd region is just now empty. Consider return to OS. */
			region_t r_dealloc = tiny_free_try_depot_unmap_no_lock(szone, tiny_mag_ptr, node);
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
			if (r_dealloc)
				deallocate_pages(szone, r_dealloc, TINY_REGION_SIZE, 0);
			return FALSE; // Caller need not unlock
		}
	}
#endif

	return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr)
}

// Allocates from the last region or a freshly allocated region
static void *
tiny_malloc_from_region_no_lock(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index,
								msize_t msize, void * aligned_address)
{
	void	*ptr;

	// Deal with unclaimed memory -- mag_bytes_free_at_end or mag_bytes_free_at_start
	if (tiny_mag_ptr->mag_bytes_free_at_end || tiny_mag_ptr->mag_bytes_free_at_start)
		tiny_finalize_region(szone, tiny_mag_ptr);

	// We set the unused bits of the header in the last pair to be all ones, and those of the inuse to zeroes.
	((tiny_region_t)aligned_address)->pairs[CEIL_NUM_TINY_BLOCKS_WORDS-1].header =
	(NUM_TINY_BLOCKS & 31) ? (0xFFFFFFFFU << (NUM_TINY_BLOCKS & 31)) : 0;
	((tiny_region_t)aligned_address)->pairs[CEIL_NUM_TINY_BLOCKS_WORDS-1].inuse = 0;

	// Here find the only place in tinyland that (infrequently) takes the tiny_regions_lock.
	// Only one thread at a time should be permitted to assess the density of the hash
	// ring and adjust if needed.
	// Only one thread at a time should be permitted to insert its new region on
	// the hash ring.
	// It is safe for all other threads to read the hash ring (hashed_regions) and
	// the associated sizes (num_regions_allocated and num_tiny_regions).

	_malloc_lock_lock(&szone->tiny_regions_lock);

	// Check to see if the hash ring of tiny regions needs to grow.  Try to
	// avoid the hash ring becoming too dense.
	if (szone->tiny_region_generation->num_regions_allocated < (2 * szone->num_tiny_regions)) {
		region_t *new_regions;
		size_t new_size;
		size_t new_shift = szone->tiny_region_generation->num_regions_allocated_shift; // In/Out parameter
		new_regions = hash_regions_grow_no_lock(szone, szone->tiny_region_generation->hashed_regions,
												szone->tiny_region_generation->num_regions_allocated,
												&new_shift,
												&new_size);
		// Do not deallocate the current hashed_regions allocation since someone may
		// be iterating it.  Instead, just leak it.

		// Prepare to advance to the "next generation" of the hash ring.
		szone->tiny_region_generation->nextgen->hashed_regions = new_regions;
		szone->tiny_region_generation->nextgen->num_regions_allocated = new_size;
		szone->tiny_region_generation->nextgen->num_regions_allocated_shift = new_shift;

		// Throw the switch to atomically advance to the next generation.
		szone->tiny_region_generation = szone->tiny_region_generation->nextgen;
		// Ensure everyone sees the advance.
		OSMemoryBarrier();
	}
	// Tag the region at "aligned_address" as belonging to us,
	// and so put it under the protection of the magazine lock we are holding.
	// Do this before advertising "aligned_address" on the hash ring(!)
	MAGAZINE_INDEX_FOR_TINY_REGION(aligned_address) = mag_index;

	// Insert the new region into the hash ring, and update malloc statistics
	hash_region_insert_no_lock(szone->tiny_region_generation->hashed_regions,
							   szone->tiny_region_generation->num_regions_allocated,
							   szone->tiny_region_generation->num_regions_allocated_shift,
							   aligned_address);

	szone->num_tiny_regions++;
	_malloc_lock_unlock(&szone->tiny_regions_lock);

	tiny_mag_ptr->mag_last_region = aligned_address;
	BYTES_USED_FOR_TINY_REGION(aligned_address) = TINY_BYTES_FOR_MSIZE(msize);
#if ASLR_INTERNAL
	int offset_msize = malloc_entropy[0] & TINY_ENTROPY_MASK;
#if DEBUG_MALLOC
	if (getenv("MallocASLRForce")) offset_msize = strtol(getenv("MallocASLRForce"), NULL, 0) & TINY_ENTROPY_MASK;
	if (getenv("MallocASLRPrint")) malloc_printf("Region: %p offset: %d\n", aligned_address, offset_msize);
#endif
#else
	int offset_msize = 0;
#endif
	ptr = (void *)((uintptr_t) aligned_address + TINY_BYTES_FOR_MSIZE(offset_msize));
	set_tiny_meta_header_in_use(ptr, msize);
	tiny_mag_ptr->mag_num_objects++;
	tiny_mag_ptr->mag_num_bytes_in_objects += TINY_BYTES_FOR_MSIZE(msize);
	tiny_mag_ptr->num_bytes_in_magazine += TINY_REGION_PAYLOAD_BYTES;

	// We put a header on the last block so that it appears in use (for coalescing, etc...)
	set_tiny_meta_header_in_use_1((void *)((uintptr_t)ptr + TINY_BYTES_FOR_MSIZE(msize)));
	tiny_mag_ptr->mag_bytes_free_at_end = TINY_BYTES_FOR_MSIZE(NUM_TINY_BLOCKS - msize - offset_msize);

#if ASLR_INTERNAL
	// Put a header on the previous block for same reason
	tiny_mag_ptr->mag_bytes_free_at_start = TINY_BYTES_FOR_MSIZE(offset_msize);
	if (offset_msize) {
		set_tiny_meta_header_in_use_1((void *)((uintptr_t)ptr - TINY_QUANTUM));
	}
#else
	tiny_mag_ptr->mag_bytes_free_at_start = 0;
#endif

	// connect to magazine as last node
	recirc_list_splice_last(szone, tiny_mag_ptr, REGION_TRAILER_FOR_TINY_REGION(aligned_address));

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in tiny_malloc_from_region_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
	}
#endif
	return ptr;
}

static INLINE void *
tiny_try_shrink_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_good_size)
{
	msize_t new_msize = TINY_MSIZE_FOR_BYTES(new_good_size);
	msize_t mshrinkage = TINY_MSIZE_FOR_BYTES(old_size) - new_msize;

	if (mshrinkage) {
		void *q = (void *)((uintptr_t)ptr + TINY_BYTES_FOR_MSIZE(new_msize));
		magazine_t *tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																	REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr)),
																	MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr)));

		// Mark q as block header and in-use, thus creating two blocks.
		set_tiny_meta_header_in_use(q, mshrinkage);
		tiny_mag_ptr->mag_num_objects++;

		SZONE_MAGAZINE_PTR_UNLOCK(szone,tiny_mag_ptr);
		szone_free(szone, q); // avoid inlining free_tiny(szone, q, ...);
	}
	return ptr;
}

static INLINE boolean_t
tiny_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
	// returns 1 on success
	msize_t	index;
	msize_t	old_msize;
	unsigned	next_index;
	void	*next_block;
	boolean_t	is_free;
	msize_t	next_msize, coalesced_msize, leftover_msize;
	void	*leftover;

	index = TINY_INDEX_FOR_PTR(ptr);
	old_msize = TINY_MSIZE_FOR_BYTES(old_size);
	next_index = index + old_msize;

	if (next_index >= NUM_TINY_BLOCKS) {
		return 0;
	}
	next_block = (char *)ptr + old_size;

	magazine_t	*tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																 REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr)),
																 MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr)));

	/*
	 * Look for a free block immediately afterwards.  If it's large enough, we can consume (part of)
	 * it.
	 */
	is_free = tiny_meta_header_is_free(next_block);
	if (!is_free) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone,tiny_mag_ptr);
		return 0; // next_block is in use;
	}
	next_msize = get_tiny_free_size(next_block);
	if (old_size + TINY_BYTES_FOR_MSIZE(next_msize) < new_size) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone,tiny_mag_ptr);
		return 0; // even with next block, not enough
	}
	/*
	 * The following block is big enough; pull it from its freelist and chop off enough to satisfy
	 * our needs.
	 */
	tiny_free_list_remove_ptr(szone, tiny_mag_ptr, next_block, next_msize);
	set_tiny_meta_header_middle(next_block); // clear the meta_header to enable coalescing backwards
	coalesced_msize = TINY_MSIZE_FOR_BYTES(new_size - old_size + TINY_QUANTUM - 1);
	leftover_msize = next_msize - coalesced_msize;
	if (leftover_msize) {
		/* there's some left, so put the remainder back */
		leftover = (void *)((uintptr_t)next_block + TINY_BYTES_FOR_MSIZE(coalesced_msize));

		tiny_free_list_add_ptr(szone, tiny_mag_ptr, leftover, leftover_msize);
	}
	set_tiny_meta_header_in_use(ptr, old_msize + coalesced_msize);
#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in tiny_try_realloc_in_place(), ptr=%p, msize=%d\n", ptr, old_msize + coalesced_msize);
	}
#endif
	tiny_mag_ptr->mag_num_bytes_in_objects += TINY_BYTES_FOR_MSIZE(coalesced_msize);

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr));
	size_t bytes_used = node->bytes_used + TINY_BYTES_FOR_MSIZE(coalesced_msize);
	node->bytes_used = bytes_used;

	// Emptiness discriminant
	if (bytes_used < DENSITY_THRESHOLD(TINY_REGION_PAYLOAD_BYTES)) {
		/* After this reallocation the region is still sparse, so it must have been even more so before
		 the reallocation. That implies the region is already correctly marked. Do nothing. */
	} else {
		/* Region has crossed threshold from sparsity to density. Mark it not "suitable" on the
		 recirculation candidates list. */
		node->recirc_suitable = FALSE;
	}

	SZONE_MAGAZINE_PTR_UNLOCK(szone,tiny_mag_ptr);
	CHECK(szone, __PRETTY_FUNCTION__);
	return 1;
}

static boolean_t
tiny_check_region(szone_t *szone, region_t region)
{
	uintptr_t	start, ptr, region_end;
	boolean_t	prev_free = 0;
	boolean_t	is_free;
	msize_t	msize;
	free_list_t	*free_head;
	void	*follower, *previous, *next;
	mag_index_t	mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(region);
	magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

	// Assumes locked
	CHECK_MAGAZINE_PTR_LOCKED(szone, tiny_mag_ptr, __PRETTY_FUNCTION__);

	/* establish region limits */
	start = (uintptr_t)TINY_REGION_ADDRESS(region);
	ptr = start;
	if (region == tiny_mag_ptr->mag_last_region) {
		ptr += tiny_mag_ptr->mag_bytes_free_at_start;

		/*
		 * Check the leading block's integrity here also.
		 */
		if (tiny_mag_ptr->mag_bytes_free_at_start) {
			msize = get_tiny_meta_header((void *)(ptr - TINY_QUANTUM), &is_free);
			if (is_free || (msize != 1)) {
				malloc_printf("*** invariant broken for leader block %p - %d %d\n", ptr - TINY_QUANTUM, msize, is_free);
			}
		}
	}
	region_end = (uintptr_t)TINY_REGION_END(region);

	/*
	 * The last region may have a trailing chunk which has not been converted into inuse/freelist
	 * blocks yet.
	 */
	if (region == tiny_mag_ptr->mag_last_region)
		region_end -= tiny_mag_ptr->mag_bytes_free_at_end;

	/*
	 * Scan blocks within the region.
	 */
	while (ptr < region_end) {
		/*
		 * If the first block is free, and its size is 65536 (msize = 0) then the entire region is
		 * free.
		 */
		msize = get_tiny_meta_header((void *)ptr, &is_free);
		if (is_free && !msize && (ptr == start)) {
			return 1;
		}

		/*
		 * If the block's size is 65536 (msize = 0) then since we're not the first entry the size is
		 * corrupt.
		 */
		if (!msize) {
			malloc_printf("*** invariant broken for tiny block %p this msize=%d - size is too small\n",
						  ptr, msize);
			return 0;
		}

		if (!is_free) {
			/*
			 * In use blocks cannot be more than (NUM_TINY_SLOTS - 1) quanta large.
			 */
			prev_free = 0;
			if (msize > (NUM_TINY_SLOTS - 1)) {
				malloc_printf("*** invariant broken for %p this tiny msize=%d - size is too large\n",
							  ptr, msize);
				return 0;
			}
			/* move to next block */
			ptr += TINY_BYTES_FOR_MSIZE(msize);
		} else {
#if !RELAXED_INVARIANT_CHECKS
			/*
			 * Free blocks must have been coalesced, we cannot have a free block following another
			 * free block.
			 */
			if (prev_free) {
				malloc_printf("*** invariant broken for free block %p this tiny msize=%d: two free blocks in a row\n",
							  ptr, msize);
				return 0;
			}
#endif // RELAXED_INVARIANT_CHECKS
			prev_free = 1;
			/*
			 * Check the integrity of this block's entry in its freelist.
			 */
			free_head = (free_list_t *)ptr;
			previous = free_list_unchecksum_ptr(szone, &free_head->previous);
			next = free_list_unchecksum_ptr(szone, &free_head->next);
			if (previous && !tiny_meta_header_is_free(previous)) {
				malloc_printf("*** invariant broken for %p (previous %p is not a free pointer)\n",
							  ptr, previous);
				return 0;
			}
			if (next && !tiny_meta_header_is_free(next)) {
				malloc_printf("*** invariant broken for %p (next in free list %p is not a free pointer)\n",
							  ptr, next);
				return 0;
			}
			/*
			 * Check the free block's trailing size value.
			 */
			follower = FOLLOWING_TINY_PTR(ptr, msize);
			if (((uintptr_t)follower != region_end) && (get_tiny_previous_free_msize(follower) != msize)) {
				malloc_printf("*** invariant broken for tiny free %p followed by %p in region [%p-%p] "
							  "(end marker incorrect) should be %d; in fact %d\n",
							  ptr, follower, TINY_REGION_ADDRESS(region), region_end, msize, get_tiny_previous_free_msize(follower));
				return 0;
			}
			/* move to next block */
			ptr = (uintptr_t)follower;
		}
	}
	/*
	 * Ensure that we scanned the entire region
	 */
	if (ptr != region_end) {
		malloc_printf("*** invariant broken for region end %p - %p\n", ptr, region_end);
		return 0;
	}
	/*
	 * Check the trailing block's integrity.
	 */
	if (region == tiny_mag_ptr->mag_last_region) {
		if (tiny_mag_ptr->mag_bytes_free_at_end) {
			msize = get_tiny_meta_header((void *)ptr, &is_free);
			if (is_free || (msize != 1)) {
				malloc_printf("*** invariant broken for blocker block %p - %d %d\n", ptr, msize, is_free);
			}
		}
	}
	return 1;
}

static kern_return_t
tiny_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone,
					   memory_reader_t reader, vm_range_recorder_t recorder)
{
	size_t		num_regions;
	size_t		index;
	region_t		*regions;
	vm_range_t		buffer[MAX_RECORDER_BUFFER];
	unsigned		count = 0;
	kern_return_t	err;
	region_t		region;
	vm_range_t		range;
	vm_range_t		admin_range;
	vm_range_t		ptr_range;
	unsigned char	*mapped_region;
	uint32_t		*block_header;
	uint32_t		*in_use;
	unsigned		block_index;
	unsigned		block_limit;
	boolean_t		is_free;
	msize_t		msize;
	void		*mapped_ptr;
	unsigned 		bit;
	magazine_t          *tiny_mag_base = NULL;

	region_hash_generation_t *trg_ptr;
	err = reader(task, (vm_address_t)szone->tiny_region_generation, sizeof(region_hash_generation_t), (void **)&trg_ptr);
	if (err) return err;

	num_regions = trg_ptr->num_regions_allocated;
	err = reader(task, (vm_address_t)trg_ptr->hashed_regions, sizeof(region_t) * num_regions, (void **)&regions);
	if (err) return err;

	if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
		// Map in all active magazines. Do this outside the iteration over regions.
		err = reader(task, (vm_address_t)(szone->tiny_magazines),
					 szone->num_tiny_magazines*sizeof(magazine_t),(void **)&tiny_mag_base);
		if (err) return err;
	}

	for (index = 0; index < num_regions; ++index) {
		region = regions[index];
		if (HASHRING_OPEN_ENTRY != region && HASHRING_REGION_DEALLOCATED != region) {
			range.address = (vm_address_t)TINY_REGION_ADDRESS(region);
			range.size = (vm_size_t)TINY_REGION_SIZE;
			if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
				admin_range.address = range.address + TINY_METADATA_START;
				admin_range.size = TINY_METADATA_SIZE;
				recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &admin_range, 1);
			}
			if (type_mask & (MALLOC_PTR_REGION_RANGE_TYPE | MALLOC_ADMIN_REGION_RANGE_TYPE)) {
				ptr_range.address = range.address;
				ptr_range.size = NUM_TINY_BLOCKS * TINY_QUANTUM;
				recorder(task, context, MALLOC_PTR_REGION_RANGE_TYPE, &ptr_range, 1);
			}
			if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
				void 		*mag_last_free;
				vm_address_t	mag_last_free_ptr = 0;
				msize_t		mag_last_free_msize = 0;

				err = reader(task, range.address, range.size, (void **)&mapped_region);
				if (err)
					return err;

				mag_index_t mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(mapped_region);
				magazine_t *tiny_mag_ptr = tiny_mag_base + mag_index;

				if (DEPOT_MAGAZINE_INDEX != mag_index) {
					mag_last_free = tiny_mag_ptr->mag_last_free;
					if (mag_last_free) {
						mag_last_free_ptr = (uintptr_t) mag_last_free & ~(TINY_QUANTUM - 1);
						mag_last_free_msize = (uintptr_t) mag_last_free & (TINY_QUANTUM - 1);
					}
				} else {
					for (mag_index = 0; mag_index < szone->num_tiny_magazines; mag_index++) {
						if ((void *)range.address == (tiny_mag_base + mag_index)->mag_last_free_rgn) {
							mag_last_free = (tiny_mag_base + mag_index)->mag_last_free;
							if (mag_last_free) {
								mag_last_free_ptr = (uintptr_t) mag_last_free & ~(TINY_QUANTUM - 1);
								mag_last_free_msize = (uintptr_t) mag_last_free & (TINY_QUANTUM - 1);
							}
						}
					}
				}

				block_header = (uint32_t *)(mapped_region + TINY_METADATA_START + sizeof(region_trailer_t));
				in_use = TINY_INUSE_FOR_HEADER(block_header);
				block_index = 0;
				block_limit = NUM_TINY_BLOCKS;
				if (region == tiny_mag_ptr->mag_last_region) {
					block_index += TINY_MSIZE_FOR_BYTES(tiny_mag_ptr->mag_bytes_free_at_start);
					block_limit -= TINY_MSIZE_FOR_BYTES(tiny_mag_ptr->mag_bytes_free_at_end);
				}

				while (block_index < block_limit) {
					vm_size_t block_offset = TINY_BYTES_FOR_MSIZE(block_index);
					is_free = !BITARRAY_BIT(in_use, block_index);
					if (is_free) {
						mapped_ptr = mapped_region + block_offset;

						// mapped_region, the address at which 'range' in 'task' has been
						// mapped into our process, is not necessarily aligned to
						// TINY_BLOCKS_ALIGN.
						//
						// Since the code in get_tiny_free_size() assumes the pointer came
						// from a properly aligned tiny region, and mapped_region is not
						// necessarily aligned, then do the size calculation directly.
						// If the next bit is set in the header bitmap, then the size is one
						// quantum.  Otherwise, read the size field.
						if (!BITARRAY_BIT(block_header, (block_index+1)))
							msize = TINY_FREE_SIZE(mapped_ptr);
						else
							msize = 1;

					} else if (range.address + block_offset != mag_last_free_ptr) {
						msize = 1;
						bit = block_index + 1;
						while (! BITARRAY_BIT(block_header, bit)) {
							bit++;
							msize ++;
						}
						buffer[count].address = range.address + block_offset;
						buffer[count].size = TINY_BYTES_FOR_MSIZE(msize);
						count++;
						if (count >= MAX_RECORDER_BUFFER) {
							recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
							count = 0;
						}
					} else {
						// Block is not free but it matches mag_last_free_ptr so even
						// though it is not marked free in the bitmap, we treat it as if
						// it is and move on
						msize = mag_last_free_msize;
					}

					if (!msize)
						return KERN_FAILURE; // Somethings amiss. Avoid looping at this block_index.

					block_index += msize;
				}
				if (count) {
					recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
					count = 0;
				}
			}
		}
	}
	return 0;
}

static void *
tiny_malloc_from_free_list(szone_t *szone, magazine_t *tiny_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	free_list_t		*ptr;
	msize_t		this_msize;
	grain_t		slot = msize - 1;
	free_list_t		**free_list = tiny_mag_ptr->mag_free_list;
	free_list_t		**the_slot = free_list + slot;
	free_list_t		*next;
	free_list_t		**limit;
#if defined(__LP64__)
	uint64_t		bitmap;
#else
	uint32_t		bitmap;
#endif
	msize_t		leftover_msize;
	free_list_t		*leftover_ptr;

	// Assumes we've locked the region
	CHECK_MAGAZINE_PTR_LOCKED(szone, tiny_mag_ptr, __PRETTY_FUNCTION__);

	// Look for an exact match by checking the freelist for this msize.
	//
	ptr = *the_slot;
	if (ptr) {
		next = free_list_unchecksum_ptr(szone, &ptr->next);
		if (next) {
			next->previous = ptr->previous;
		} else {
			BITMAPV_CLR(tiny_mag_ptr->mag_bitmap, slot);
		}
		*the_slot = next;
		this_msize = msize;
#if DEBUG_MALLOC
		if (LOG(szone, ptr)) {
			malloc_printf("in tiny_malloc_from_free_list(), exact match ptr=%p, this_msize=%d\n", ptr, this_msize);
		}
#endif
		goto return_tiny_alloc;
	}

	// Mask off the bits representing slots holding free blocks smaller than the
	// size we need.  If there are no larger free blocks, try allocating from
	// the free space at the end of the tiny region.
#if defined(__LP64__)
	bitmap = ((uint64_t *)(tiny_mag_ptr->mag_bitmap))[0] & ~ ((1ULL << slot) - 1);
#else
	bitmap = tiny_mag_ptr->mag_bitmap[0] & ~ ((1 << slot) - 1);
#endif
	if (!bitmap)
		goto try_tiny_malloc_from_end;

	slot = BITMAPV_CTZ(bitmap);
	limit = free_list + NUM_TINY_SLOTS - 1;
	free_list += slot;

	if (free_list < limit) {
		ptr = *free_list;
		if (ptr) {
			next = free_list_unchecksum_ptr(szone, &ptr->next);
			*free_list = next;
			if (next) {
				next->previous = ptr->previous;
			} else {
				BITMAPV_CLR(tiny_mag_ptr->mag_bitmap, slot);
			}
			this_msize = get_tiny_free_size(ptr);
			goto add_leftover_and_proceed;
		}
#if DEBUG_MALLOC
		malloc_printf("in tiny_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n",slot);
#endif
	}

	// We are now looking at the last slot, which contains blocks equal to, or
	// due to coalescing of free blocks, larger than (NUM_TINY_SLOTS - 1) * tiny quantum size.
	// If the last freelist is not empty, and the head contains a block that is
	// larger than our request, then the remainder is put back on the free list.
	ptr = *limit;
	if (ptr) {
		this_msize = get_tiny_free_size(ptr);
		next = free_list_unchecksum_ptr(szone, &ptr->next);
		if (this_msize - msize >= NUM_TINY_SLOTS) {
			// the leftover will go back to the free list, so we optimize by
			// modifying the free list rather than a pop and push of the head
			leftover_msize = this_msize - msize;
			leftover_ptr = (free_list_t *)((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize));
			*limit = leftover_ptr;
			if (next) {
				next->previous.u = free_list_checksum_ptr(szone, leftover_ptr);
			}
			leftover_ptr->previous = ptr->previous;
			leftover_ptr->next = ptr->next;
			set_tiny_meta_header_free(leftover_ptr, leftover_msize);
#if DEBUG_MALLOC
			if (LOG(szone,ptr)) {
				malloc_printf("in tiny_malloc_from_free_list(), last slot ptr=%p, msize=%d this_msize=%d\n",
							  ptr, msize, this_msize);
			}
#endif
			this_msize = msize;
			goto return_tiny_alloc;
		}
		if (next) {
			next->previous = ptr->previous;
		}
		*limit = next;
		goto add_leftover_and_proceed;
		/* NOTREACHED */
	}

try_tiny_malloc_from_end:
	// Let's see if we can use tiny_mag_ptr->mag_bytes_free_at_end
	if (tiny_mag_ptr->mag_bytes_free_at_end >= TINY_BYTES_FOR_MSIZE(msize)) {
		ptr = (free_list_t *)((uintptr_t)TINY_REGION_END(tiny_mag_ptr->mag_last_region) -
							  tiny_mag_ptr->mag_bytes_free_at_end);
		tiny_mag_ptr->mag_bytes_free_at_end -= TINY_BYTES_FOR_MSIZE(msize);
		if (tiny_mag_ptr->mag_bytes_free_at_end) {
			// let's add an in use block after ptr to serve as boundary
			set_tiny_meta_header_in_use_1((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize));
		}
		this_msize = msize;
#if DEBUG_MALLOC
		if (LOG(szone, ptr)) {
			malloc_printf("in tiny_malloc_from_free_list(), from end ptr=%p, msize=%d\n", ptr, msize);
		}
#endif
		goto return_tiny_alloc;
	}
#if ASLR_INTERNAL
	// Try from start if nothing left at end
	if (tiny_mag_ptr->mag_bytes_free_at_start >= TINY_BYTES_FOR_MSIZE(msize)) {
		ptr = (free_list_t *)(TINY_REGION_ADDRESS(tiny_mag_ptr->mag_last_region) +
							  tiny_mag_ptr->mag_bytes_free_at_start - TINY_BYTES_FOR_MSIZE(msize));
		tiny_mag_ptr->mag_bytes_free_at_start -= TINY_BYTES_FOR_MSIZE(msize);
		if (tiny_mag_ptr->mag_bytes_free_at_start) {
			// let's add an in use block before ptr to serve as boundary
			set_tiny_meta_header_in_use_1((unsigned char *)ptr - TINY_QUANTUM);
		}
		this_msize = msize;
#if DEBUG_MALLOC
		if (LOG(szone, ptr)) {
			malloc_printf("in tiny_malloc_from_free_list(), from start ptr=%p, msize=%d\n", ptr, msize);
		}
#endif
		goto return_tiny_alloc;
	}
#endif
	return NULL;

add_leftover_and_proceed:
	if (!this_msize || (this_msize > msize)) {
		leftover_msize = this_msize - msize;
		leftover_ptr = (free_list_t *)((unsigned char *)ptr + TINY_BYTES_FOR_MSIZE(msize));
#if DEBUG_MALLOC
		if (LOG(szone,ptr)) {
			malloc_printf("in tiny_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
		}
#endif
		tiny_free_list_add_ptr(szone, tiny_mag_ptr, leftover_ptr, leftover_msize);
		this_msize = msize;
	}

return_tiny_alloc:
	tiny_mag_ptr->mag_num_objects++;
	tiny_mag_ptr->mag_num_bytes_in_objects += TINY_BYTES_FOR_MSIZE(this_msize);

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr));
	size_t bytes_used = node->bytes_used + TINY_BYTES_FOR_MSIZE(this_msize);
	node->bytes_used = bytes_used;

	// Emptiness discriminant
	if (bytes_used < DENSITY_THRESHOLD(TINY_REGION_PAYLOAD_BYTES)) {
		/* After this allocation the region is still sparse, so it must have been even more so before
		 the allocation. That implies the region is already correctly marked. Do nothing. */
	} else {
		/* Region has crossed threshold from sparsity to density. Mark it not "suitable" on the
		 recirculation candidates list. */
		node->recirc_suitable = FALSE;
	}
#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in tiny_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
	}
#endif
	if (this_msize > 1)
		set_tiny_meta_header_in_use(ptr, this_msize);
	else
		set_tiny_meta_header_in_use_1(ptr);
	return ptr;
}
#undef DENSITY_THRESHOLD
#undef K

static INLINE void *
tiny_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested)
{
	void	*ptr;
	mag_index_t	mag_index = mag_get_thread_index(szone);
	magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

#if DEBUG_MALLOC
	if (DEPOT_MAGAZINE_INDEX == mag_index) {
		szone_error(szone, 1, "malloc called for magazine index -1", NULL, NULL);
		return(NULL);
	}

	if (!msize) {
		szone_error(szone, 1, "invariant broken (!msize) in allocation (region)", NULL, NULL);
		return(NULL);
	}
#endif

	SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);

#if TINY_CACHE
	ptr = tiny_mag_ptr->mag_last_free;

	if ((((uintptr_t)ptr) & (TINY_QUANTUM - 1)) == msize) {
		// we have a winner
		tiny_mag_ptr->mag_last_free = NULL;
		tiny_mag_ptr->mag_last_free_rgn = NULL;
		SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
		CHECK(szone, __PRETTY_FUNCTION__);
		ptr = (void *)((uintptr_t)ptr & ~ (TINY_QUANTUM - 1));
		if (cleared_requested) {
			memset(ptr, 0, TINY_BYTES_FOR_MSIZE(msize));
		}
#if DEBUG_MALLOC
		if (LOG(szone,ptr)) {
			malloc_printf("in tiny_malloc_should_clear(), tiny cache ptr=%p, msize=%d\n", ptr, msize);
		}
#endif
		return ptr;
	}
#endif /* TINY_CACHE */

	while (1) {
		ptr = tiny_malloc_from_free_list(szone, tiny_mag_ptr, mag_index, msize);
		if (ptr) {
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
			CHECK(szone, __PRETTY_FUNCTION__);
			if (cleared_requested) {
				memset(ptr, 0, TINY_BYTES_FOR_MSIZE(msize));
			}
			return ptr;
		}

		if (tiny_get_region_from_depot(szone, tiny_mag_ptr, mag_index, msize)) {
			ptr = tiny_malloc_from_free_list(szone, tiny_mag_ptr, mag_index, msize);
			if (ptr) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				CHECK(szone, __PRETTY_FUNCTION__);
				if (cleared_requested) {
					memset(ptr, 0, TINY_BYTES_FOR_MSIZE(msize));
				}
				return ptr;
			}
		}

		// The magazine is exhausted. A new region (heap) must be allocated to satisfy this call to malloc().
		// The allocation, an mmap() system call, will be performed outside the magazine spin locks by the first
		// thread that suffers the exhaustion. That thread sets "alloc_underway" and enters a critical section.
		// Threads arriving here later are excluded from the critical section, yield the CPU, and then retry the
		// allocation. After some time the magazine is resupplied, the original thread leaves with its allocation,
		// and retry-ing threads succeed in the code just above.
		if (!tiny_mag_ptr->alloc_underway) {
			void *fresh_region;

			// time to create a new region (do this outside the magazine lock)
			tiny_mag_ptr->alloc_underway = TRUE;
			OSMemoryBarrier();
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
			fresh_region = allocate_pages_securely(szone, TINY_REGION_SIZE, TINY_BLOCKS_ALIGN, VM_MEMORY_MALLOC_TINY);
			SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);

			MAGMALLOC_ALLOCREGION((void *)szone, (int)mag_index, fresh_region, TINY_REGION_SIZE); // DTrace USDT Probe

			if (!fresh_region) { // out of memory!
				tiny_mag_ptr->alloc_underway = FALSE;
				OSMemoryBarrier();
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				return NULL;
			}

			ptr = tiny_malloc_from_region_no_lock(szone, tiny_mag_ptr, mag_index, msize, fresh_region);

			// we don't clear because this freshly allocated space is pristine
			tiny_mag_ptr->alloc_underway = FALSE;
			OSMemoryBarrier();
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
			CHECK(szone, __PRETTY_FUNCTION__);
			return ptr;
		} else {
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
			yield();
			SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);
		}
	}
	/* NOTREACHED */
}

static NOINLINE void
free_tiny_botch(szone_t *szone, free_list_t *ptr)
{
	mag_index_t mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr));
	magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);
	SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
	szone_error(szone, 1, "double free", ptr, NULL);
}

static INLINE void
free_tiny(szone_t *szone, void *ptr, region_t tiny_region, size_t known_size)
{
	msize_t	msize;
	boolean_t	is_free;
	mag_index_t mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(tiny_region);
	magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

	// ptr is known to be in tiny_region
	if (known_size) {
		msize = TINY_MSIZE_FOR_BYTES(known_size + TINY_QUANTUM - 1);
	} else {
		msize = get_tiny_meta_header(ptr, &is_free);
		if (is_free) {
			free_tiny_botch(szone, ptr);
			return;
		}
	}
#if DEBUG_MALLOC
	if (!msize) {
		malloc_printf("*** free_tiny() block in use is too large: %p\n", ptr);
		return;
	}
#endif

	SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);

#if TINY_CACHE
	// Depot does not participate in TINY_CACHE since it can't be directly malloc()'d
	if (DEPOT_MAGAZINE_INDEX != mag_index) {
		if (msize < TINY_QUANTUM) { // to see if the bits fit in the last 4 bits
			void *ptr2 = tiny_mag_ptr->mag_last_free; // Might be NULL
			region_t rgn2 = tiny_mag_ptr->mag_last_free_rgn;

			/* check that we don't already have this pointer in the cache */
			if (ptr == (void *)((uintptr_t)ptr2 & ~ (TINY_QUANTUM - 1))) {
				free_tiny_botch(szone, ptr);
				return;
			}

			if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && msize)
				memset(ptr, SCRABBLE_BYTE, TINY_BYTES_FOR_MSIZE(msize));

			tiny_mag_ptr->mag_last_free = (void *)(((uintptr_t)ptr) | msize);
			tiny_mag_ptr->mag_last_free_rgn = tiny_region;

			if (!ptr2) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				CHECK(szone, __PRETTY_FUNCTION__);
				return;
			}

			msize = (uintptr_t)ptr2 & (TINY_QUANTUM - 1);
			ptr = (void *)(((uintptr_t)ptr2) & ~(TINY_QUANTUM - 1));
			tiny_region = rgn2;
		}
	}
#endif /* TINY_CACHE */

	// Now in the time it took to acquire the lock, the region may have migrated
	// from one magazine to another. I.e. trailer->mag_index is volatile.
	// In which case the magazine lock we obtained (namely magazines[mag_index].mag_lock)
	// is stale. If so, keep on tryin' ...
	region_trailer_t *trailer = REGION_TRAILER_FOR_TINY_REGION(tiny_region);
	mag_index_t refreshed_index;

	while (mag_index != (refreshed_index = trailer->mag_index)) { // Note assignment

		SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);

		mag_index = refreshed_index;
		tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);
		SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);
	}

	if (tiny_free_no_lock(szone, tiny_mag_ptr, mag_index, tiny_region, ptr, msize))
		SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);

	CHECK(szone, __PRETTY_FUNCTION__);
}

static void
print_tiny_free_list(szone_t *szone)
{
	free_list_t	*ptr;
	_SIMPLE_STRING b = _simple_salloc();
	mag_index_t mag_index;

	if (b) {
		_simple_sappend(b, "tiny free sizes:\n");
		for (mag_index = -1; mag_index < szone->num_tiny_magazines; mag_index++) {
			grain_t	slot = 0;
			_simple_sprintf(b,"\tMagazine %d: ", mag_index);
			while (slot < NUM_TINY_SLOTS) {
				ptr = szone->tiny_magazines[mag_index].mag_free_list[slot];
				if (ptr) {
					_simple_sprintf(b, "%s%y[%d]; ", (slot == NUM_TINY_SLOTS-1) ? ">=" : "",
									(slot+1)*TINY_QUANTUM, free_list_count(szone, ptr));
				}
				slot++;
			}
			_simple_sappend(b,"\n");
		}
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
		_simple_sfree(b);
	}
}

static void
print_tiny_region(boolean_t verbose, region_t region, size_t bytes_at_start, size_t bytes_at_end)
{
	unsigned		counts[1024];
	unsigned		in_use = 0;
	uintptr_t		start = (uintptr_t)TINY_REGION_ADDRESS(region);
	uintptr_t		current = start + bytes_at_end;
	uintptr_t		limit =  (uintptr_t)TINY_REGION_END(region) - bytes_at_end;
	boolean_t		is_free;
	msize_t		msize;
	unsigned		ci;
	_SIMPLE_STRING	b;
	uintptr_t		pgTot = 0;

	if (region == HASHRING_REGION_DEALLOCATED) {
		if ((b = _simple_salloc()) != NULL) {
			_simple_sprintf(b, "Tiny region [unknown address] was returned to the OS\n");
			_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
			_simple_sfree(b);
		}
		return;
	}

	memset(counts, 0, sizeof(counts));
	while (current < limit) {
		msize = get_tiny_meta_header((void *)current, &is_free);
		if (is_free & !msize && (current == start)) {
			// first block is all free
			uintptr_t pgLo = round_page_quanta(start + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(start + TINY_REGION_SIZE - sizeof(msize_t));

			if (pgLo < pgHi) {
				pgTot += (pgHi - pgLo);
			}
			break;
		}
		if (!msize) {
			malloc_printf("*** error with %p: msize=%d\n", (void *)current, (unsigned)msize);
			break;
		}
		if (!is_free) {
			// block in use
			if (msize > NUM_TINY_SLOTS)
				malloc_printf("*** error at %p msize for in_use is %d\n", (void *)current, msize);
			if (msize < 1024)
				counts[msize]++;
			in_use++;
		} else {
			uintptr_t pgLo = round_page_quanta(current + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(current + TINY_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));

			if (pgLo < pgHi) {
				pgTot += (pgHi - pgLo);
			}
		}
		current += TINY_BYTES_FOR_MSIZE(msize);
	}
	if ((b = _simple_salloc()) != NULL) {
		_simple_sprintf(b, "Tiny region [%p-%p, %y] \t", (void *)start, TINY_REGION_END(region), (int)TINY_REGION_SIZE);
		_simple_sprintf(b, "Magazine=%d \t", MAGAZINE_INDEX_FOR_TINY_REGION(region));
		_simple_sprintf(b, "Allocations in use=%d \t Bytes in use=%ly \t", in_use, BYTES_USED_FOR_TINY_REGION(region));
		if (bytes_at_end || bytes_at_start)
			_simple_sprintf(b, "Untouched=%ly ", bytes_at_end + bytes_at_start);
		if (DEPOT_MAGAZINE_INDEX == MAGAZINE_INDEX_FOR_TINY_REGION(region)) {
			_simple_sprintf(b, "Advised MADV_FREE=%ly", pgTot);
		} else {
			_simple_sprintf(b, "Fragments subject to reclamation=%ly", pgTot);
		}
		if (verbose && in_use) {
			_simple_sappend(b, "\n\tSizes in use: ");
			for (ci = 0; ci < 1024; ci++)
				if (counts[ci])
					_simple_sprintf(b, "%d[%d] ", TINY_BYTES_FOR_MSIZE(ci), counts[ci]);
		}
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
		_simple_sfree(b);
	}
}

static boolean_t
tiny_free_list_check(szone_t *szone, grain_t slot)
{
	mag_index_t mag_index;

	for (mag_index = -1; mag_index < szone->num_tiny_magazines; mag_index++) {
		magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);
		SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);

		unsigned	count = 0;
		free_list_t	*ptr = szone->tiny_magazines[mag_index].mag_free_list[slot];
		boolean_t	is_free;
		free_list_t	*previous = NULL;

		while (ptr) {
			is_free = tiny_meta_header_is_free(ptr);
			if (! is_free) {
				malloc_printf("*** in-use ptr in free list slot=%d count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				return 0;
			}
			if (((uintptr_t)ptr) & (TINY_QUANTUM - 1)) {
				malloc_printf("*** unaligned ptr in free list slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				return 0;
			}
			if (!tiny_region_for_ptr_no_lock(szone, ptr)) {
				malloc_printf("*** ptr not in szone slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				return 0;
			}
			if (free_list_unchecksum_ptr(szone, &ptr->previous) != previous) {
				malloc_printf("*** previous incorrectly set slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				return 0;
			}
			previous = ptr;
			ptr = free_list_unchecksum_ptr(szone, &ptr->next);
			count++;
		}

		SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
	}
	return 1;
}

/*********************	SMALL FREE LIST UTILITIES	************************/

/*
 * Mark a block as free.  Only the first quantum of a block is marked thusly,
 * the remainder are marked "middle".
 */
static INLINE void
small_meta_header_set_is_free(msize_t *meta_headers, unsigned index, msize_t msize)
{
	meta_headers[index] = msize | SMALL_IS_FREE;
}

/*
 * Mark a block as in use.  Only the first quantum of a block is marked thusly,
 * the remainder are marked "middle".
 */
static INLINE void
small_meta_header_set_in_use(msize_t *meta_headers, msize_t index, msize_t msize)
{
	meta_headers[index] = msize;
}

/*
 * Mark a quantum as being the second or later in a block.
 */
static INLINE void
small_meta_header_set_middle(msize_t *meta_headers, msize_t index)
{
	meta_headers[index] = 0;
}

/*
 * Adds an item to the proper free list, and also marks the meta-header of the
 * block properly.
 * Assumes szone has been locked
 */
static void
small_free_list_add_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
{
	grain_t	slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
	free_list_t	*free_ptr = ptr;
	free_list_t	*free_head = small_mag_ptr->mag_free_list[slot];
	void	*follower;

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
	}
	if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
		szone_error(szone, 1, "small_free_list_add_ptr: Unaligned ptr", ptr, NULL);
	}
#endif
	small_meta_header_set_is_free(SMALL_META_HEADER_FOR_PTR(ptr), SMALL_META_INDEX_FOR_PTR(ptr), msize);

	if (free_head) {
#if DEBUG_MALLOC
		if (free_list_unchecksum_ptr(szone, &free_head->previous)) {
			szone_error(szone, 1, "small_free_list_add_ptr: Internal invariant broken (free_head->previous)", ptr,
						"ptr=%p slot=%d free_head=%p previous=%p\n", ptr, slot, (void *)free_head, free_head->previous.p);
		}
		if (!SMALL_PTR_IS_FREE(free_head)) {
			szone_error(szone, 1, "small_free_list_add_ptr: Internal invariant broken (free_head is not a free pointer)", ptr,
						"ptr=%p slot=%d free_head=%p\n", ptr, slot, (void *)free_head);
		}
#endif
		free_head->previous.u = free_list_checksum_ptr(szone, free_ptr);
	} else {
		BITMAPN_SET(small_mag_ptr->mag_bitmap, slot);
	}
	free_ptr->previous.u = free_list_checksum_ptr(szone, NULL);
	free_ptr->next.u = free_list_checksum_ptr(szone, free_head);

	small_mag_ptr->mag_free_list[slot] = free_ptr;

	// Store msize at the end of the block denoted by "ptr" (i.e. at a negative offset from "follower")
	follower = (void *)((uintptr_t)ptr + SMALL_BYTES_FOR_MSIZE(msize));
	SMALL_PREVIOUS_MSIZE(follower) = msize;
}

/*
 * Removes the item pointed to by ptr in the proper free list.
 * Assumes szone has been locked
 */
static void
small_free_list_remove_ptr(szone_t *szone, magazine_t *small_mag_ptr, void *ptr, msize_t msize)
{
	grain_t	slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
	free_list_t	*free_ptr = ptr, *next, *previous;

	next = free_list_unchecksum_ptr(szone, &free_ptr->next);
	previous = free_list_unchecksum_ptr(szone, &free_ptr->previous);

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("In %s, ptr=%p, msize=%d\n", __FUNCTION__, ptr, msize);
	}
#endif

	if (!previous) {
		// The block to remove is the head of the free list
#if DEBUG_MALLOC
		if (small_mag_ptr->mag_free_list[slot] != ptr) {
			szone_error(szone, 1, "small_free_list_remove_ptr: Internal invariant broken (small_mag_ptr->mag_free_list[slot])", ptr,
						"ptr=%p slot=%d msize=%d small_mag_ptr->mag_free_list[slot]=%p\n",
						ptr, slot, msize, (void *)small_mag_ptr->mag_free_list[slot]);
			return;
		}
#endif
		small_mag_ptr->mag_free_list[slot] = next;
		if (!next) BITMAPN_CLR(small_mag_ptr->mag_bitmap, slot);
	} else {
		// We know free_ptr is already checksummed, so we don't need to do it
		// again.
		previous->next = free_ptr->next;
	}
	if (next) {
		// We know free_ptr is already checksummed, so we don't need to do it
		// again.
		next->previous = free_ptr->previous;
	}
}

/*
 * small_region_for_ptr_no_lock - Returns the small region containing the pointer,
 * or NULL if not found.
 */
static INLINE region_t
small_region_for_ptr_no_lock(szone_t *szone, const void *ptr)
{
	rgnhdl_t r = hash_lookup_region_no_lock(szone->small_region_generation->hashed_regions,
											szone->small_region_generation->num_regions_allocated,
											szone->small_region_generation->num_regions_allocated_shift,
											SMALL_REGION_FOR_PTR(ptr));
	return r ? *r : r;
}

static void
small_finalize_region(szone_t *szone, magazine_t *small_mag_ptr) {
	void      *last_block, *previous_block;
	msize_t   last_msize, previous_msize, last_index;

	// It is possible that the block prior to the last block in the region has
	// been free'd, but was not coalesced with the free bytes at the end of the
	// block, since we treat the bytes at the end of the region as "in use" in
	// the meta headers. Attempt to coalesce the last block with the previous
	// block, so we don't violate the "no consecutive free blocks" invariant.
	//
	// FIXME: If we could calculate the previous small free size in the same
	//        manner as tiny_previous_preceding_free, it would eliminate the
	//        index & previous msize checks, which are a guard against reading
	//        bogus data out of in-use or written-on-freed memory.
	//
	// FIXME: Need to investigate how much work would be required to increase
	//        'mag_bytes_free_at_end' when freeing the preceding block, rather
	//        than performing this workaround.
	//
	if (small_mag_ptr->mag_bytes_free_at_end) {
		last_block = SMALL_REGION_END(small_mag_ptr->mag_last_region) - small_mag_ptr->mag_bytes_free_at_end;
		last_msize = SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end);

		last_index = SMALL_META_INDEX_FOR_PTR(last_block);
		previous_msize = SMALL_PREVIOUS_MSIZE(last_block);

		if (last_index && (previous_msize <= last_index)) {
			previous_block = (void *)((uintptr_t)last_block - SMALL_BYTES_FOR_MSIZE(previous_msize));
			if (*SMALL_METADATA_FOR_PTR(previous_block) == (previous_msize | SMALL_IS_FREE)) {
				msize_t *meta_headers = SMALL_META_HEADER_FOR_PTR(last_block);

				small_meta_header_set_middle(meta_headers, last_index);
				small_free_list_remove_ptr(szone, small_mag_ptr, previous_block, previous_msize);
				last_block = (void *)((uintptr_t)last_block - SMALL_BYTES_FOR_MSIZE(previous_msize));
				last_msize += previous_msize;
			}
		}

		// splice last_block into the free list
		small_free_list_add_ptr(szone, small_mag_ptr, last_block, last_msize);
		small_mag_ptr->mag_bytes_free_at_end = 0;
	}

#if ASLR_INTERNAL
	if (small_mag_ptr->mag_bytes_free_at_start) {
		last_block = SMALL_REGION_ADDRESS(small_mag_ptr->mag_last_region);
		last_msize = SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start);

		void *next_block = (void *) ((uintptr_t)last_block + small_mag_ptr->mag_bytes_free_at_start);
		if (SMALL_PTR_IS_FREE(next_block)) {
			msize_t next_msize = SMALL_PTR_SIZE(next_block);

			small_meta_header_set_middle(SMALL_META_HEADER_FOR_PTR(next_block), SMALL_META_INDEX_FOR_PTR(next_block));
			small_free_list_remove_ptr(szone, small_mag_ptr, next_block, next_msize);
			last_msize += next_msize;
		}

		// splice last_block into the free list
		small_free_list_add_ptr(szone, small_mag_ptr, last_block, last_msize);
		small_mag_ptr->mag_bytes_free_at_start = 0;
	}
#endif

	// TODO: Will we ever need to coalesce the blocks at the beginning and end when we finalize?

	small_mag_ptr->mag_last_region = NULL;
}

static int
small_free_detach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r) {
	unsigned char	*ptr = SMALL_REGION_ADDRESS(r);
	msize_t		*meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
	uintptr_t		start = (uintptr_t)SMALL_REGION_ADDRESS(r);
	uintptr_t		current = start;
	uintptr_t		limit =  (uintptr_t)SMALL_REGION_END(r);
	int			total_alloc = 0;

	while (current < limit) {
		unsigned	index = SMALL_META_INDEX_FOR_PTR(current);
		msize_t		msize_and_free = meta_headers[index];
		boolean_t	is_free = msize_and_free & SMALL_IS_FREE;
		msize_t		msize = msize_and_free & ~ SMALL_IS_FREE;

		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** small_free_detach_region error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			small_free_list_remove_ptr(szone, small_mag_ptr, (void *)current, msize);
		} else {
			total_alloc++;
		}
		current += SMALL_BYTES_FOR_MSIZE(msize);
	}
	return total_alloc;
}

static size_t
small_free_reattach_region(szone_t *szone, magazine_t *small_mag_ptr, region_t r) {
	unsigned char	*ptr = SMALL_REGION_ADDRESS(r);
	msize_t		*meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
	uintptr_t		start = (uintptr_t)SMALL_REGION_ADDRESS(r);
	uintptr_t		current = start;
	uintptr_t		limit =  (uintptr_t)SMALL_REGION_END(r);
	size_t		total_alloc = 0;

	while (current < limit) {
		unsigned	index = SMALL_META_INDEX_FOR_PTR(current);
		msize_t		msize_and_free = meta_headers[index];
		boolean_t	is_free = msize_and_free & SMALL_IS_FREE;
		msize_t		msize = msize_and_free & ~ SMALL_IS_FREE;

		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** small_free_reattach_region error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			small_free_list_add_ptr(szone, small_mag_ptr, (void *)current, msize);
		} else {
			total_alloc += SMALL_BYTES_FOR_MSIZE(msize);
		}
		current += SMALL_BYTES_FOR_MSIZE(msize);
	}
	return total_alloc;
}

typedef struct {
	uint16_t pnum, size;
} small_pg_pair_t;

static void NOINLINE /* want private stack frame for automatic array */
small_free_scan_madvise_free(szone_t *szone, magazine_t *depot_ptr, region_t r) {
	uintptr_t	start = (uintptr_t)SMALL_REGION_ADDRESS(r);
	uintptr_t	current = start;
	uintptr_t	limit =  (uintptr_t)SMALL_REGION_END(r);
	msize_t	*meta_headers = SMALL_META_HEADER_FOR_PTR(start);
	small_pg_pair_t advisory[((SMALL_REGION_PAYLOAD_BYTES + vm_page_quanta_size - 1) >> vm_page_quanta_shift) >> 1]; // 4096bytes stack allocated
	int		advisories = 0;

	// Scan the metadata identifying blocks which span one or more pages. Mark the pages MADV_FREE taking care to preserve free list
	// management data.
	while (current < limit) {
		unsigned	index = SMALL_META_INDEX_FOR_PTR(current);
		msize_t		msize_and_free = meta_headers[index];
		boolean_t	is_free = msize_and_free & SMALL_IS_FREE;
		msize_t		msize = msize_and_free & ~ SMALL_IS_FREE;

		if (is_free && !msize && (current == start)) {
#if DEBUG_MALLOC
			// first block is all free
			malloc_printf("*** small_free_scan_madvise_free first block is all free! %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			uintptr_t pgLo = round_page_quanta(start + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(start + SMALL_REGION_SIZE - sizeof(msize_t));

			if (pgLo < pgHi) {
				advisory[advisories].pnum = (pgLo - start) >> vm_page_quanta_shift;
				advisory[advisories].size = (pgHi - pgLo) >> vm_page_quanta_shift;
				advisories++;
			}
			break;
		}
		if (!msize) {
#if DEBUG_MALLOC
			malloc_printf("*** small_free_scan_madvise_free error with %p: msize=%d is_free =%d\n",
						  (void *)current, msize, is_free);
#endif
			break;
		}
		if (is_free) {
			uintptr_t pgLo = round_page_quanta(current + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(current + SMALL_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));

			if (pgLo < pgHi) {
				advisory[advisories].pnum = (pgLo - start) >> vm_page_quanta_shift;
				advisory[advisories].size = (pgHi - pgLo) >> vm_page_quanta_shift;
				advisories++;
			}
		}
		current += SMALL_BYTES_FOR_MSIZE(msize);
	}

	if (advisories > 0) {
		int i;

		OSAtomicIncrement32Barrier(&(REGION_TRAILER_FOR_SMALL_REGION(r)->pinned_to_depot));
		SZONE_MAGAZINE_PTR_UNLOCK(szone, depot_ptr);
		for (i = 0; i < advisories; ++i) {
			uintptr_t addr = (advisory[i].pnum << vm_page_quanta_shift) + start;
			size_t size = advisory[i].size << vm_page_quanta_shift;

			madvise_free_range(szone, r, addr, addr + size, NULL);
		}
		SZONE_MAGAZINE_PTR_LOCK(szone, depot_ptr);
		OSAtomicDecrement32Barrier(&(REGION_TRAILER_FOR_SMALL_REGION(r)->pinned_to_depot));
	}
}

static region_t
small_free_try_depot_unmap_no_lock(szone_t *szone, magazine_t *depot_ptr, region_trailer_t *node)
{
	if (0 < node->bytes_used ||
		0 < node->pinned_to_depot ||
		depot_ptr->recirculation_entries < (szone->num_small_magazines * 2)) {
		return NULL;
	}

	// disconnect first node from Depot
	recirc_list_extract(szone, depot_ptr, node);

	// Iterate the region pulling its free entries off the (locked) Depot's free list
	region_t sparse_region = SMALL_REGION_FOR_PTR(node);
	int objects_in_use = small_free_detach_region(szone, depot_ptr, sparse_region);

	if (0 == objects_in_use) {
		// Invalidate the hash table entry for this region with HASHRING_REGION_DEALLOCATED.
		// Using HASHRING_REGION_DEALLOCATED preserves the collision chain, using HASHRING_OPEN_ENTRY (0) would not.
		rgnhdl_t pSlot = hash_lookup_region_no_lock(szone->small_region_generation->hashed_regions,
													szone->small_region_generation->num_regions_allocated,
													szone->small_region_generation->num_regions_allocated_shift, sparse_region);
		if (NULL == pSlot) {
			szone_error(szone, 1, "small_free_try_depot_unmap_no_lock hash lookup failed:", NULL, "%p\n", sparse_region);
			return NULL;
		}
		*pSlot = HASHRING_REGION_DEALLOCATED;
		depot_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
		__sync_fetch_and_add( &(szone->num_small_regions_dealloc), 1); // Atomically increment num_small_regions_dealloc

		// Caller will transfer ownership of the region back to the OS with no locks held
		MAGMALLOC_DEALLOCREGION((void *)szone, (void *)sparse_region, SMALL_REGION_SIZE); // DTrace USDT Probe
		return sparse_region;

	} else {
		szone_error(szone, 1, "small_free_try_depot_unmap_no_lock objects_in_use not zero:", NULL, "%d\n", objects_in_use);
		return NULL;
	}
}

static boolean_t
small_free_do_recirc_to_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index)
{
	// The entire magazine crossed the "emptiness threshold". Transfer a region
	// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
	// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.
	region_trailer_t *node = small_mag_ptr->firstNode;

	while (node && !node->recirc_suitable) {
		node = node->next;
	}

	if (NULL == node) {
#if DEBUG_MALLOC
		malloc_printf("*** small_free_do_recirc_to_depot end of list\n");
#endif
		return TRUE; // Caller must SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
	}

	region_t sparse_region = SMALL_REGION_FOR_PTR(node);

	// Deal with unclaimed memory -- mag_bytes_free_at_end or mag_bytes_free_at start
	if (sparse_region == small_mag_ptr->mag_last_region && (small_mag_ptr->mag_bytes_free_at_end || small_mag_ptr->mag_bytes_free_at_start)) {
		small_finalize_region(szone, small_mag_ptr);
	}

	// disconnect "suitable" node from magazine
	recirc_list_extract(szone, small_mag_ptr, node);

	// Iterate the region pulling its free entries off its (locked) magazine's free list
	int objects_in_use = small_free_detach_region(szone, small_mag_ptr, sparse_region);
	magazine_t *depot_ptr = &(szone->small_magazines[DEPOT_MAGAZINE_INDEX]);

	// hand over the region to the (locked) Depot
	SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);
	// this will cause small_free_list_add_ptr called by small_free_reattach_region to use
	// the depot as its target magazine, rather than magazine formerly associated with sparse_region
	MAGAZINE_INDEX_FOR_SMALL_REGION(sparse_region) = DEPOT_MAGAZINE_INDEX;
	node->pinned_to_depot = 0;

	// Iterate the region putting its free entries on Depot's free list
	size_t bytes_inplay = small_free_reattach_region(szone, depot_ptr, sparse_region);

	small_mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
	small_mag_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
	small_mag_ptr->mag_num_objects -= objects_in_use;

	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr); // Unlock the originating magazine

	depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
	depot_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
	depot_ptr->mag_num_objects += objects_in_use;

	// connect to Depot as last node
	recirc_list_splice_last(szone, depot_ptr, node);

	MAGMALLOC_RECIRCREGION((void *)szone, (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
						   (int)BYTES_USED_FOR_SMALL_REGION(sparse_region)); // DTrace USDT Probe

	// Mark free'd dirty pages with MADV_FREE to reduce memory pressure
	small_free_scan_madvise_free(szone, depot_ptr, sparse_region);

	// If the region is entirely empty vm_deallocate() it outside the depot lock
	region_t r_dealloc = small_free_try_depot_unmap_no_lock(szone, depot_ptr, node);
	SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
	if (r_dealloc)
		deallocate_pages(szone, r_dealloc, SMALL_REGION_SIZE, 0);
	return FALSE; // Caller need not unlock the originating magazine
}

static region_t
small_find_msize_region(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	free_list_t		*ptr;
	grain_t		slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
	free_list_t		**free_list = small_mag_ptr->mag_free_list;
	free_list_t		**the_slot = free_list + slot;
	free_list_t		**limit;
	unsigned		bitmap;

	// Assumes we've locked the magazine
	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);

	// Look for an exact match by checking the freelist for this msize.
	ptr = *the_slot;
	if (ptr)
		return SMALL_REGION_FOR_PTR(ptr);

	// Mask off the bits representing slots holding free blocks smaller than
	// the size we need.
	if (szone->is_largemem) {
		// BITMAPN_CTZ implementation
		unsigned idx = slot >> 5;
		bitmap = 0;
		unsigned mask = ~ ((1 << (slot & 31)) - 1);
		for ( ; idx < SMALL_BITMAP_WORDS; ++idx ) {
			bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
			if (bitmap != 0)
				break;
			mask = ~0U;
		}
		// Check for fallthrough: No bits set in bitmap
		if ((bitmap == 0) && (idx == SMALL_BITMAP_WORDS))
			return NULL;

		// Start looking at the first set bit, plus 32 bits for every word of
		// zeroes or entries that were too small.
		slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
	} else {
		bitmap = small_mag_ptr->mag_bitmap[0] & ~ ((1 << slot) - 1);
		if (!bitmap)
			return NULL;

		slot = BITMAP32_CTZ((&bitmap));
	}
	limit = free_list + szone->num_small_slots - 1;
	free_list += slot;

	if (free_list < limit) {
		ptr = *free_list;
		if (ptr)
			return SMALL_REGION_FOR_PTR(ptr);
		else {
			/* Shouldn't happen. Fall through to look at last slot. */
#if DEBUG_MALLOC
			malloc_printf("in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n",slot);
#endif
		}
	}

	// We are now looking at the last slot, which contains blocks equal to, or
	// due to coalescing of free blocks, larger than (num_small_slots - 1) * (small quantum size).
	ptr = *limit;
	if (ptr)
		return SMALL_REGION_FOR_PTR(ptr);

	return NULL;
}

static boolean_t
small_get_region_from_depot(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	magazine_t *depot_ptr = &(szone->small_magazines[DEPOT_MAGAZINE_INDEX]);

	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
	if (szone->num_small_magazines == 1) // Uniprocessor, single magazine, so no recirculation necessary
		return 0;

#if DEBUG_MALLOC
	if (DEPOT_MAGAZINE_INDEX == mag_index) {
		szone_error(szone, 1, "small_get_region_from_depot called for magazine index -1", NULL, NULL);
		return 0;
	}
#endif

	SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);

	// Appropriate a Depot'd region that can satisfy requested msize.
	region_trailer_t *node;
	region_t sparse_region;

	while (1) {
		sparse_region = small_find_msize_region(szone, depot_ptr, DEPOT_MAGAZINE_INDEX, msize);
		if (NULL == sparse_region) { // Depot empty?
			SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
			return 0;
		}

		node = REGION_TRAILER_FOR_SMALL_REGION(sparse_region);
		if (0 >= node->pinned_to_depot)
			break;

		SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);
		yield();
		SZONE_MAGAZINE_PTR_LOCK(szone,depot_ptr);
	}

	// disconnect node from Depot
	recirc_list_extract(szone, depot_ptr, node);

	// Iterate the region pulling its free entries off the (locked) Depot's free list
	int objects_in_use = small_free_detach_region(szone, depot_ptr, sparse_region);

	// Transfer ownership of the region
	MAGAZINE_INDEX_FOR_SMALL_REGION(sparse_region) = mag_index;
	node->pinned_to_depot = 0;

	// Iterate the region putting its free entries on its new (locked) magazine's free list
	size_t bytes_inplay = small_free_reattach_region(szone, small_mag_ptr, sparse_region);

	depot_ptr->mag_num_bytes_in_objects -= bytes_inplay;
	depot_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
	depot_ptr->mag_num_objects -= objects_in_use;

	small_mag_ptr->mag_num_bytes_in_objects += bytes_inplay;
	small_mag_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
	small_mag_ptr->mag_num_objects += objects_in_use;

	// connect to magazine as first node
	recirc_list_splice_first(szone, small_mag_ptr, node);

	SZONE_MAGAZINE_PTR_UNLOCK(szone,depot_ptr);

	// madvise() outside the Depot lock
	(void)madvise_reuse_range(szone, sparse_region, sparse_region, sparse_region+SMALL_REGION_PAYLOAD_BYTES);

	MAGMALLOC_DEPOTREGION((void *)szone, (int)mag_index, (void *)sparse_region, SMALL_REGION_SIZE,
						  (int)BYTES_USED_FOR_SMALL_REGION(sparse_region)); // DTrace USDT Probe

	return 1;
}

#define K 1.5 // headroom measured in number of 8Mb regions
#define DENSITY_THRESHOLD(a) \
	((a) - ((a) >> 2)) // "Emptiness" f = 0.25, so "Density" is (1 - f)*a. Generally: ((a) - ((a) >> -log2(f)))

static INLINE boolean_t
small_free_no_lock(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, region_t region, void *ptr, msize_t msize)
{
	msize_t		*meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
	unsigned		index = SMALL_META_INDEX_FOR_PTR(ptr);
	void		*original_ptr = ptr;
	size_t		original_size = SMALL_BYTES_FOR_MSIZE(msize);
	unsigned char	*next_block = ((unsigned char *)ptr + original_size);
	msize_t		next_index = index + msize;
	msize_t		previous_msize, next_msize;
	void		*previous;

#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
	}
	if (!msize) {
		szone_error(szone, 1, "trying to free small block that is too small", ptr,
					"in small_free_no_lock(), ptr=%p, msize=%d\n", ptr, msize);
	}
#endif

	// We try to coalesce this block with the preceeding one
	if (index && (SMALL_PREVIOUS_MSIZE(ptr) <= index)) {
		previous_msize = SMALL_PREVIOUS_MSIZE(ptr);
		if (meta_headers[index - previous_msize] == (previous_msize | SMALL_IS_FREE)) {
			previous = (void *)((uintptr_t)ptr - SMALL_BYTES_FOR_MSIZE(previous_msize));
			// previous is really to be coalesced
#if DEBUG_MALLOC
			if (LOG(szone, ptr) || LOG(szone,previous)) {
				malloc_printf("in small_free_no_lock(), coalesced backwards for %p previous=%p\n", ptr, previous);
			}
#endif
			small_free_list_remove_ptr(szone, small_mag_ptr, previous, previous_msize);
			small_meta_header_set_middle(meta_headers, index);
			ptr = previous;
			msize += previous_msize;
			index -= previous_msize;
		}
	}
	// We try to coalesce with the next block
	if ((next_block < SMALL_REGION_END(region)) && (meta_headers[next_index] & SMALL_IS_FREE)) {
		// next block is free, we coalesce
		next_msize = meta_headers[next_index] & ~ SMALL_IS_FREE;
#if DEBUG_MALLOC
		if (LOG(szone,ptr))
			malloc_printf("In small_free_no_lock(), for ptr=%p, msize=%d coalesced next block=%p next_msize=%d\n",
						  ptr, msize, next_block, next_msize);
#endif
		small_free_list_remove_ptr(szone, small_mag_ptr, next_block, next_msize);
		small_meta_header_set_middle(meta_headers, next_index);
		msize += next_msize;
	}
	if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) {
		if (!msize) {
			szone_error(szone, 1, "incorrect size information - block header was damaged", ptr, NULL);
		} else {
			memset(ptr, SCRABBLE_BYTE, SMALL_BYTES_FOR_MSIZE(msize));
		}
	}
	small_free_list_add_ptr(szone, small_mag_ptr, ptr, msize);
	small_mag_ptr->mag_num_objects--;
	// we use original_size and not msize to avoid double counting the coalesced blocks
	small_mag_ptr->mag_num_bytes_in_objects -= original_size;

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(region);
	size_t bytes_used = node->bytes_used - original_size;
	node->bytes_used = bytes_used;

#if !TARGET_OS_EMBEDDED // Always madvise for embedded platforms
	/* FIXME: Would Uniprocessor benefit from recirc and MADV_FREE? */
	if (szone->num_small_magazines == 1) { // Uniprocessor, single magazine, so no recirculation necessary
		/* NOTHING */
	} else if (DEPOT_MAGAZINE_INDEX != mag_index) {
		// Emptiness discriminant
		if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
			/* Region has crossed threshold from density to sparsity. Mark it "suitable" on the
			 recirculation candidates list. */
			node->recirc_suitable = TRUE;
		} else {
			/* After this free, we've found the region is still dense, so it must have been even more so before
			 the free. That implies the region is already correctly marked. Do nothing. */
		}

		// Has the entire magazine crossed the "emptiness threshold"? If so, transfer a region
		// from this magazine to the Depot. Choose a region that itself has crossed the emptiness threshold (i.e
		// is at least fraction "f" empty.) Such a region will be marked "suitable" on the recirculation list.

		size_t a = small_mag_ptr->num_bytes_in_magazine; // Total bytes allocated to this magazine
		size_t u = small_mag_ptr->mag_num_bytes_in_objects; // In use (malloc'd) from this magaqzine

		if (a - u > ((3 * SMALL_REGION_PAYLOAD_BYTES) / 2) && u < DENSITY_THRESHOLD(a)) {
			return small_free_do_recirc_to_depot(szone, small_mag_ptr, mag_index);
		}

	} else {
#endif
		// Freed to Depot. N.B. Lock on small_magazines[DEPOT_MAGAZINE_INDEX] is already held
		// Calcuate the first page in the coalesced block that would be safe to mark MADV_FREE
		size_t free_header_size = sizeof(free_list_t) + sizeof(msize_t);
		uintptr_t safe_ptr = (uintptr_t)ptr + free_header_size;
		uintptr_t round_safe = round_page_quanta(safe_ptr);

		// Calcuate the last page in the coalesced block that would be safe to mark MADV_FREE
		size_t free_tail_size = sizeof(msize_t);
		uintptr_t safe_extent = (uintptr_t)ptr + SMALL_BYTES_FOR_MSIZE(msize) - free_tail_size;
		uintptr_t trunc_extent = trunc_page_quanta(safe_extent);

		// The newly freed block may complete a span of bytes that cover one or more pages. Mark the span with MADV_FREE.
		if (round_safe < trunc_extent) { // Coalesced area covers a page (perhaps many)
			// Extend the freed block by the free region header and tail sizes to include pages
			// we may have coalesced that no longer host free region tails and headers.
			// This may extend over in-use ranges, but the MIN/MAX clamping below will fix that up.
			uintptr_t lo = trunc_page_quanta((uintptr_t)original_ptr - free_tail_size);
			uintptr_t hi = round_page_quanta((uintptr_t)original_ptr + original_size + free_header_size);

			uintptr_t free_lo = MAX(round_safe, lo);
			uintptr_t free_hi = MIN(trunc_extent, hi);

			if (free_lo < free_hi) {
				small_free_list_remove_ptr(szone, small_mag_ptr, ptr, msize);
				small_meta_header_set_in_use(meta_headers, index, msize);

				OSAtomicIncrement32Barrier(&(node->pinned_to_depot));
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				madvise_free_range(szone, region, free_lo, free_hi, &szone->last_small_advise);
				SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
				OSAtomicDecrement32Barrier(&(node->pinned_to_depot));

				small_meta_header_set_is_free(meta_headers, index, msize);
				small_free_list_add_ptr(szone, small_mag_ptr, ptr, msize);
			}
		}

#if !TARGET_OS_EMBEDDED
		if (0 < bytes_used || 0 < node->pinned_to_depot) {
			/* Depot'd region is still live. Leave it in place on the Depot's recirculation list
			 so as to avoid thrashing between the Depot's free list and a magazines's free list
			 with detach_region/reattach_region */
		} else {
			/* Depot'd region is just now empty. Consider return to OS. */
			region_t r_dealloc = small_free_try_depot_unmap_no_lock(szone, small_mag_ptr, node);
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			if (r_dealloc)
				deallocate_pages(szone, r_dealloc, SMALL_REGION_SIZE, 0);
			return FALSE; // Caller need not unlock
		}
	}
#endif

	return TRUE; // Caller must do SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr)
}

// Allocates from the last region or a freshly allocated region
static void *
small_malloc_from_region_no_lock(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index,
								 msize_t msize, void *aligned_address)
{
	void	*ptr;

	// Before anything we transform the mag_bytes_free_at_end or mag_bytes_free_at_start - if any - to a regular free block
	/* FIXME: last_block needs to be coalesced with previous entry if free, <rdar://5462322> */
	if (small_mag_ptr->mag_bytes_free_at_end || small_mag_ptr->mag_bytes_free_at_start)
		small_finalize_region(szone, small_mag_ptr);

	// Here find the only place in smallville that (infrequently) takes the small_regions_lock.
	// Only one thread at a time should be permitted to assess the density of the hash
	// ring and adjust if needed.
	// Only one thread at a time should be permitted to insert its new region on
	// the hash ring.
	// It is safe for all other threads to read the hash ring (hashed_regions) and
	// the associated sizes (num_regions_allocated and num_small_regions).

	_malloc_lock_lock(&szone->small_regions_lock);
	// Check to see if the hash ring of small regions needs to grow.  Try to
	// avoid the hash ring becoming too dense.
	if (szone->small_region_generation->num_regions_allocated < (2 * szone->num_small_regions)) {
		region_t *new_regions;
		size_t new_size;
		size_t new_shift = szone->small_region_generation->num_regions_allocated_shift; // In/Out parameter
		new_regions = hash_regions_grow_no_lock(szone, szone->small_region_generation->hashed_regions,
												szone->small_region_generation->num_regions_allocated,
												&new_shift,
												&new_size);
		// Do not deallocate the current hashed_regions allocation since someone
		// may be iterating it.  Instead, just leak it.

		// Prepare to advance to the "next generation" of the hash ring.
		szone->small_region_generation->nextgen->hashed_regions = new_regions;
		szone->small_region_generation->nextgen->num_regions_allocated = new_size;
		szone->small_region_generation->nextgen->num_regions_allocated_shift = new_shift;

		// Throw the switch to atomically advance to the next generation.
		szone->small_region_generation = szone->small_region_generation->nextgen;
		// Ensure everyone sees the advance.
		OSMemoryBarrier();
	}
	// Tag the region at "aligned_address" as belonging to us,
	// and so put it under the protection of the magazine lock we are holding.
	// Do this before advertising "aligned_address" on the hash ring(!)
	MAGAZINE_INDEX_FOR_SMALL_REGION(aligned_address) = mag_index;

	// Insert the new region into the hash ring, and update malloc statistics
	hash_region_insert_no_lock(szone->small_region_generation->hashed_regions,
							   szone->small_region_generation->num_regions_allocated,
							   szone->small_region_generation->num_regions_allocated_shift,
							   aligned_address);

	szone->num_small_regions++;

	_malloc_lock_unlock(&szone->small_regions_lock);

	small_mag_ptr->mag_last_region = aligned_address;
	BYTES_USED_FOR_SMALL_REGION(aligned_address) = SMALL_BYTES_FOR_MSIZE(msize);
#if ASLR_INTERNAL
	int offset_msize = malloc_entropy[1] & SMALL_ENTROPY_MASK;
#if DEBUG_MALLOC
	if (getenv("MallocASLRForce")) offset_msize = strtol(getenv("MallocASLRForce"), NULL, 0) & SMALL_ENTROPY_MASK;
	if (getenv("MallocASLRPrint")) malloc_printf("Region: %p offset: %d\n", aligned_address, offset_msize);
#endif
#else
	int offset_msize = 0;
#endif
	ptr = (void *)((uintptr_t) aligned_address + SMALL_BYTES_FOR_MSIZE(offset_msize));
	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), offset_msize, msize);
	small_mag_ptr->mag_num_objects++;
	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(msize);
	small_mag_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;

	// add a big free block at the end
	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), offset_msize + msize, NUM_SMALL_BLOCKS - msize - offset_msize);
	small_mag_ptr->mag_bytes_free_at_end = SMALL_BYTES_FOR_MSIZE(NUM_SMALL_BLOCKS - msize - offset_msize);

#if ASLR_INTERNAL
	// add a big free block at the start
	small_mag_ptr->mag_bytes_free_at_start = SMALL_BYTES_FOR_MSIZE(offset_msize);
	if (offset_msize) {
		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), 0, offset_msize);
	}
#else
	small_mag_ptr->mag_bytes_free_at_start = 0;
#endif

	// connect to magazine as last node
	recirc_list_splice_last(szone, small_mag_ptr, REGION_TRAILER_FOR_SMALL_REGION(aligned_address));

	return ptr;
}

static INLINE void *
small_try_shrink_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_good_size)
{
	msize_t new_msize = SMALL_MSIZE_FOR_BYTES(new_good_size);
	msize_t mshrinkage = SMALL_MSIZE_FOR_BYTES(old_size) - new_msize;

	if (mshrinkage) {
		void *q = (void *)((uintptr_t)ptr + SMALL_BYTES_FOR_MSIZE(new_msize));
		magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
																	 REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)),
																	 MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));

		// Mark q as block header and in-use, thus creating two blocks.
		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), SMALL_META_INDEX_FOR_PTR(ptr), new_msize);
		small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), mshrinkage);
		small_mag_ptr->mag_num_objects++;

		SZONE_MAGAZINE_PTR_UNLOCK(szone,small_mag_ptr);
		szone_free(szone, q); // avoid inlining free_small(szone, q, ...);
	}

	return ptr;
}

static INLINE boolean_t
small_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
	// returns 1 on success
	msize_t	*meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
	unsigned	index;
	msize_t	old_msize, new_msize;
	unsigned	next_index;
	void	*next_block;
	msize_t	next_msize_and_free;
	boolean_t	is_free;
	msize_t	next_msize, leftover_msize;
	void	*leftover;

	index = SMALL_META_INDEX_FOR_PTR(ptr);
	old_msize = SMALL_MSIZE_FOR_BYTES(old_size);
	new_msize = SMALL_MSIZE_FOR_BYTES(new_size + SMALL_QUANTUM - 1);
	next_index = index + old_msize;

	if (next_index >= NUM_SMALL_BLOCKS) {
		return 0;
	}
	next_block = (char *)ptr + old_size;

#if DEBUG_MALLOC
	if ((uintptr_t)next_block & (SMALL_QUANTUM - 1)) {
		szone_error(szone, 1, "internal invariant broken in realloc(next_block)", next_block, NULL);
	}
	if (meta_headers[index] != old_msize)
		malloc_printf("*** small_try_realloc_in_place incorrect old %d %d\n",
					  meta_headers[index], old_msize);
#endif

	magazine_t	*small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
																  REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)),
																  MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr)));

	/*
	 * Look for a free block immediately afterwards.  If it's large enough, we can consume (part of)
	 * it.
	 */
	next_msize_and_free = meta_headers[next_index];
	is_free = next_msize_and_free & SMALL_IS_FREE;
	if (!is_free) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
		return 0; // next_block is in use;
	}
	next_msize = next_msize_and_free & ~ SMALL_IS_FREE;
	if (old_msize + next_msize < new_msize) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
		return 0; // even with next block, not enough
	}
	/*
	 * The following block is big enough; pull it from its freelist and chop off enough to satisfy
	 * our needs.
	 */
	small_free_list_remove_ptr(szone, small_mag_ptr, next_block, next_msize);
	small_meta_header_set_middle(meta_headers, next_index);
	leftover_msize = old_msize + next_msize - new_msize;
	if (leftover_msize) {
		/* there's some left, so put the remainder back */
		leftover = (unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(new_msize);

		small_free_list_add_ptr(szone, small_mag_ptr, leftover, leftover_msize);
	}
#if DEBUG_MALLOC
	if (SMALL_BYTES_FOR_MSIZE(new_msize) > szone->large_threshold) {
		malloc_printf("*** realloc in place for %p exceeded msize=%d\n", new_msize);
	}
#endif
	small_meta_header_set_in_use(meta_headers, index, new_msize);
#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in small_try_realloc_in_place(), ptr=%p, msize=%d\n", ptr, *SMALL_METADATA_FOR_PTR(ptr));
	}
#endif
	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(new_msize - old_msize);

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
	size_t bytes_used = node->bytes_used + SMALL_BYTES_FOR_MSIZE(new_msize - old_msize);
	node->bytes_used = bytes_used;

	// Emptiness discriminant
	if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
		/* After this reallocation the region is still sparse, so it must have been even more so before
		 the reallocation. That implies the region is already correctly marked. Do nothing. */
	} else {
		/* Region has crossed threshold from sparsity to density. Mark it not "suitable" on the
		 recirculation candidates list. */
		node->recirc_suitable = FALSE;
	}

	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
	CHECK(szone, __PRETTY_FUNCTION__);
	return 1;
}

static boolean_t
small_check_region(szone_t *szone, region_t region)
{
	unsigned char	*ptr = SMALL_REGION_ADDRESS(region);
	msize_t		*meta_headers = SMALL_META_HEADER_FOR_PTR(ptr);
	unsigned char	*region_end = SMALL_REGION_END(region);
	msize_t		prev_free = 0;
	unsigned		index;
	msize_t		msize_and_free;
	msize_t		msize;
	free_list_t		*free_head;
	void		*previous, *next;
	msize_t		*follower;
	mag_index_t		mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
	magazine_t		*small_mag_ptr = &(szone->small_magazines[mag_index]);

	// Assumes locked
	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);

	if (region == small_mag_ptr->mag_last_region) {
		ptr += small_mag_ptr->mag_bytes_free_at_start;
		region_end -= small_mag_ptr->mag_bytes_free_at_end;
	}

	while (ptr < region_end) {
		index = SMALL_META_INDEX_FOR_PTR(ptr);
		msize_and_free = meta_headers[index];
		if (!(msize_and_free & SMALL_IS_FREE)) {
			// block is in use
			msize = msize_and_free;
			if (!msize) {
				malloc_printf("*** invariant broken: null msize ptr=%p num_small_regions=%d end=%p\n",
							  ptr, szone->num_small_regions, region_end);
				return 0;
			}
#if !RELAXED_INVARIANT_CHECKS
			if (SMALL_BYTES_FOR_MSIZE(msize) > szone->large_threshold) {
				malloc_printf("*** invariant broken for %p this small msize=%d - size is too large\n",
							  ptr, msize_and_free);
				return 0;
			}
#endif // RELAXED_INVARIANT_CHECKS
			ptr += SMALL_BYTES_FOR_MSIZE(msize);
			prev_free = 0;
		} else {
			// free pointer
			msize = msize_and_free & ~ SMALL_IS_FREE;
			free_head = (free_list_t *)ptr;
			follower = (msize_t *)FOLLOWING_SMALL_PTR(ptr, msize);
			if (!msize) {
				malloc_printf("*** invariant broken for free block %p this msize=%d\n", ptr, msize);
				return 0;
			}
#if !RELAXED_INVARIANT_CHECKS
			if (prev_free) {
				malloc_printf("*** invariant broken for %p (2 free in a row)\n", ptr);
				return 0;
			}
#endif
			previous = free_list_unchecksum_ptr(szone, &free_head->previous);
			next = free_list_unchecksum_ptr(szone, &free_head->next);
			if (previous && !SMALL_PTR_IS_FREE(previous)) {
				malloc_printf("*** invariant broken for %p (previous %p is not a free pointer)\n",
							  ptr, free_head->previous);
				return 0;
			}
			if (next && !SMALL_PTR_IS_FREE(next)) {
				malloc_printf("*** invariant broken for %p (next is not a free pointer)\n", ptr);
				return 0;
			}
			if (SMALL_PREVIOUS_MSIZE(follower) != msize) {
				malloc_printf("*** invariant broken for small free %p followed by %p in region [%p-%p] "
							  "(end marker incorrect) should be %d; in fact %d\n",
							  ptr, follower, SMALL_REGION_ADDRESS(region), region_end, msize, SMALL_PREVIOUS_MSIZE(follower));
				return 0;
			}
			ptr = (unsigned char *)follower;
			prev_free = SMALL_IS_FREE;
		}
	}
	return 1;
}

static kern_return_t
small_in_use_enumerator(task_t task, void *context, unsigned type_mask, szone_t *szone,
						memory_reader_t reader, vm_range_recorder_t recorder)
{
	size_t		num_regions;
	size_t		index;
	region_t		*regions;
	vm_range_t		buffer[MAX_RECORDER_BUFFER];
	unsigned		count = 0;
	kern_return_t	err;
	region_t		region;
	vm_range_t		range;
	vm_range_t		admin_range;
	vm_range_t		ptr_range;
	unsigned char	*mapped_region;
	msize_t		*block_header;
	unsigned		block_index;
	unsigned		block_limit;
	msize_t		msize_and_free;
	msize_t		msize;
	magazine_t          *small_mag_base = NULL;

	region_hash_generation_t *srg_ptr;
	err = reader(task, (vm_address_t)szone->small_region_generation, sizeof(region_hash_generation_t), (void **)&srg_ptr);
	if (err) return err;

	num_regions = srg_ptr->num_regions_allocated;
	err = reader(task, (vm_address_t)srg_ptr->hashed_regions, sizeof(region_t) * num_regions, (void **)&regions);
	if (err) return err;

	if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
		// Map in all active magazines. Do this outside the iteration over regions.
		err = reader(task, (vm_address_t)(szone->small_magazines),
					 szone->num_small_magazines*sizeof(magazine_t),(void **)&small_mag_base);
		if (err) return err;
	}

	for (index = 0; index < num_regions; ++index) {
		region = regions[index];
		if (HASHRING_OPEN_ENTRY != region && HASHRING_REGION_DEALLOCATED != region) {
			range.address = (vm_address_t)SMALL_REGION_ADDRESS(region);
			range.size = SMALL_REGION_SIZE;
			if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
				admin_range.address = range.address + SMALL_METADATA_START;
				admin_range.size = SMALL_METADATA_SIZE;
				recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &admin_range, 1);
			}
			if (type_mask & (MALLOC_PTR_REGION_RANGE_TYPE | MALLOC_ADMIN_REGION_RANGE_TYPE)) {
				ptr_range.address = range.address;
				ptr_range.size = NUM_SMALL_BLOCKS * SMALL_QUANTUM;
				recorder(task, context, MALLOC_PTR_REGION_RANGE_TYPE, &ptr_range, 1);
			}
			if (type_mask & MALLOC_PTR_IN_USE_RANGE_TYPE) {
				void 		*mag_last_free;
				vm_address_t	mag_last_free_ptr = 0;
				msize_t		mag_last_free_msize = 0;

				err = reader(task, range.address, range.size, (void **)&mapped_region);
				if (err)
					return err;

				mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(mapped_region);
				magazine_t *small_mag_ptr = small_mag_base + mag_index;

				if (DEPOT_MAGAZINE_INDEX != mag_index) {
					mag_last_free = small_mag_ptr->mag_last_free;
					if (mag_last_free) {
						mag_last_free_ptr = (uintptr_t) mag_last_free & ~(SMALL_QUANTUM - 1);
						mag_last_free_msize = (uintptr_t) mag_last_free & (SMALL_QUANTUM - 1);
					}
				} else {
					for (mag_index = 0; mag_index < szone->num_small_magazines; mag_index++) {
						if ((void *)range.address == (small_mag_base + mag_index)->mag_last_free_rgn) {
							mag_last_free = (small_mag_base + mag_index)->mag_last_free;
							if (mag_last_free) {
								mag_last_free_ptr = (uintptr_t) mag_last_free & ~(SMALL_QUANTUM - 1);
								mag_last_free_msize = (uintptr_t) mag_last_free & (SMALL_QUANTUM - 1);
							}
						}
					}
				}

				block_header = (msize_t *)(mapped_region + SMALL_METADATA_START + sizeof(region_trailer_t));
				block_index = 0;
				block_limit = NUM_SMALL_BLOCKS;
				if (region == small_mag_ptr->mag_last_region) {
					block_index += SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start);
					block_limit -= SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end);
				}
				while (block_index < block_limit) {
					msize_and_free = block_header[block_index];
					msize = msize_and_free & ~ SMALL_IS_FREE;
					if (! (msize_and_free & SMALL_IS_FREE) &&
						range.address + SMALL_BYTES_FOR_MSIZE(block_index) != mag_last_free_ptr) {
						// Block in use
						buffer[count].address = range.address + SMALL_BYTES_FOR_MSIZE(block_index);
						buffer[count].size = SMALL_BYTES_FOR_MSIZE(msize);
						count++;
						if (count >= MAX_RECORDER_BUFFER) {
							recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
							count = 0;
						}
					}

					if (!msize)
						return KERN_FAILURE; // Somethings amiss. Avoid looping at this block_index.

					block_index += msize;
				}
				if (count) {
					recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE, buffer, count);
					count = 0;
				}
			}
		}
	}
	return 0;
}

static void *
small_malloc_from_free_list(szone_t *szone, magazine_t *small_mag_ptr, mag_index_t mag_index, msize_t msize)
{
	free_list_t		*ptr;
	msize_t		this_msize;
	grain_t		slot = (msize <= szone->num_small_slots) ? msize - 1 : szone->num_small_slots - 1;
	free_list_t		**free_list = small_mag_ptr->mag_free_list;
	free_list_t		**the_slot = free_list + slot;
	free_list_t		*next;
	free_list_t		**limit;
	unsigned		bitmap;
	msize_t		leftover_msize;
	free_list_t		*leftover_ptr;

	// Assumes we've locked the region
	CHECK_MAGAZINE_PTR_LOCKED(szone, small_mag_ptr, __PRETTY_FUNCTION__);

	// Look for an exact match by checking the freelist for this msize.
	//
	ptr = *the_slot;
	if (ptr) {
		next = free_list_unchecksum_ptr(szone, &ptr->next);
		if (next) {
			next->previous = ptr->previous;
		} else {
			BITMAPN_CLR(small_mag_ptr->mag_bitmap, slot);
		}
		*the_slot = next;
		this_msize = msize;
		goto return_small_alloc;
	}

	// Mask off the bits representing slots holding free blocks smaller than
	// the size we need.  If there are no larger free blocks, try allocating
	// from the free space at the end of the small region.
	if (szone->is_largemem) {
		// BITMAPN_CTZ implementation
		unsigned idx = slot >> 5;
		bitmap = 0;
		unsigned mask = ~ ((1 << (slot & 31)) - 1);
		for ( ; idx < SMALL_BITMAP_WORDS; ++idx ) {
			bitmap = small_mag_ptr->mag_bitmap[idx] & mask;
			if (bitmap != 0)
				break;
			mask = ~0U;
		}
		// Check for fallthrough: No bits set in bitmap
		if ((bitmap == 0) && (idx == SMALL_BITMAP_WORDS))
			goto try_small_from_end;

		// Start looking at the first set bit, plus 32 bits for every word of
		// zeroes or entries that were too small.
		slot = BITMAP32_CTZ((&bitmap)) + (idx * 32);
	} else {
		bitmap = small_mag_ptr->mag_bitmap[0] & ~ ((1 << slot) - 1);
		if (!bitmap)
			goto try_small_from_end;

		slot = BITMAP32_CTZ((&bitmap));
	}
	// FIXME: Explain use of - 1 here, last slot has special meaning
	limit = free_list + szone->num_small_slots - 1;
	free_list += slot;

	if (free_list < limit) {
		ptr = *free_list;
		if (ptr) {

			next = free_list_unchecksum_ptr(szone, &ptr->next);
			*free_list = next;
			if (next) {
				next->previous = ptr->previous;
			} else {
				BITMAPN_CLR(small_mag_ptr->mag_bitmap, slot);
			}
			this_msize = SMALL_PTR_SIZE(ptr);
			goto add_leftover_and_proceed;
		}
#if DEBUG_MALLOC
		malloc_printf("in small_malloc_from_free_list(), mag_bitmap out of sync, slot=%d\n",slot);
#endif
	}

	// We are now looking at the last slot, which contains blocks equal to, or
	// due to coalescing of free blocks, larger than (num_small_slots - 1) * (small quantum size).
	// If the last freelist is not empty, and the head contains a block that is
	// larger than our request, then the remainder is put back on the free list.
	//
	ptr = *limit;
	if (ptr) {
		this_msize = SMALL_PTR_SIZE(ptr);
		next = free_list_unchecksum_ptr(szone, &ptr->next);
		if (this_msize - msize >= szone->num_small_slots) {
			// the leftover will go back to the free list, so we optimize by
			// modifying the free list rather than a pop and push of the head
			leftover_msize = this_msize - msize;
			leftover_ptr = (free_list_t *)((unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize));
			*limit = leftover_ptr;
			if (next) {
				next->previous.u = free_list_checksum_ptr(szone, leftover_ptr);
			}
			leftover_ptr->previous = ptr->previous;
			leftover_ptr->next = ptr->next;
			small_meta_header_set_is_free(SMALL_META_HEADER_FOR_PTR(leftover_ptr),
										  SMALL_META_INDEX_FOR_PTR(leftover_ptr), leftover_msize);
			// Store msize at the end of the block denoted by "leftover_ptr" (i.e. at a negative offset from follower)
			SMALL_PREVIOUS_MSIZE(FOLLOWING_SMALL_PTR(leftover_ptr, leftover_msize)) = leftover_msize; // Access is safe
#if DEBUG_MALLOC
			if (LOG(szone,ptr)) {
				malloc_printf("in small_malloc_from_free_list(), last slot ptr=%p, msize=%d this_msize=%d\n", ptr, msize, this_msize);
			}
#endif
			this_msize = msize;
			goto return_small_alloc;
		}
		if (next) {
			next->previous = ptr->previous;
		}
		*limit = next;
		goto add_leftover_and_proceed;
	}

try_small_from_end:
	// Let's see if we can use small_mag_ptr->mag_bytes_free_at_end
	if (small_mag_ptr->mag_bytes_free_at_end >= SMALL_BYTES_FOR_MSIZE(msize)) {
		ptr = (free_list_t *)(SMALL_REGION_END(small_mag_ptr->mag_last_region) -
							  small_mag_ptr->mag_bytes_free_at_end);
		small_mag_ptr->mag_bytes_free_at_end -= SMALL_BYTES_FOR_MSIZE(msize);
		if (small_mag_ptr->mag_bytes_free_at_end) {
			// let's mark this block as in use to serve as boundary
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr),
										 SMALL_META_INDEX_FOR_PTR((unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize)),
										 SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_end));
		}
		this_msize = msize;
		goto return_small_alloc;
	}
#if ASLR_INTERNAL
	// Try from start if nothing left at end
	if (small_mag_ptr->mag_bytes_free_at_start >= SMALL_BYTES_FOR_MSIZE(msize)) {
		ptr = (free_list_t *)(SMALL_REGION_ADDRESS(small_mag_ptr->mag_last_region) +
							  small_mag_ptr->mag_bytes_free_at_start - SMALL_BYTES_FOR_MSIZE(msize));
		small_mag_ptr->mag_bytes_free_at_start -= SMALL_BYTES_FOR_MSIZE(msize);
		if (small_mag_ptr->mag_bytes_free_at_start) {
			// let's mark this block as in use to serve as boundary
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), 0, SMALL_MSIZE_FOR_BYTES(small_mag_ptr->mag_bytes_free_at_start));
		}
		this_msize = msize;
		goto return_small_alloc;
	}
#endif
	return NULL;

add_leftover_and_proceed:
	if (this_msize > msize) {
		leftover_msize = this_msize - msize;
		leftover_ptr = (free_list_t *)((unsigned char *)ptr + SMALL_BYTES_FOR_MSIZE(msize));
#if DEBUG_MALLOC
		if (LOG(szone,ptr)) {
			malloc_printf("in small_malloc_from_free_list(), adding leftover ptr=%p, this_msize=%d\n", ptr, this_msize);
		}
#endif
		small_free_list_add_ptr(szone, small_mag_ptr, leftover_ptr, leftover_msize);
		this_msize = msize;
	}

return_small_alloc:
	small_mag_ptr->mag_num_objects++;
	small_mag_ptr->mag_num_bytes_in_objects += SMALL_BYTES_FOR_MSIZE(this_msize);

	// Update this region's bytes in use count
	region_trailer_t *node = REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
	size_t bytes_used = node->bytes_used + SMALL_BYTES_FOR_MSIZE(this_msize);
	node->bytes_used = bytes_used;

	// Emptiness discriminant
	if (bytes_used < DENSITY_THRESHOLD(SMALL_REGION_PAYLOAD_BYTES)) {
		/* After this allocation the region is still sparse, so it must have been even more so before
		 the allocation. That implies the region is already correctly marked. Do nothing. */
	} else {
		/* Region has crossed threshold from sparsity to density. Mark in not "suitable" on the
		 recirculation candidates list. */
		node->recirc_suitable = FALSE;
	}
#if DEBUG_MALLOC
	if (LOG(szone,ptr)) {
		malloc_printf("in small_malloc_from_free_list(), ptr=%p, this_msize=%d, msize=%d\n", ptr, this_msize, msize);
	}
#endif
	small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(ptr), SMALL_META_INDEX_FOR_PTR(ptr), this_msize);
	return ptr;
}
#undef DENSITY_THRESHOLD
#undef K

static INLINE void *
small_malloc_should_clear(szone_t *szone, msize_t msize, boolean_t cleared_requested)
{
	void	*ptr;
	mag_index_t	mag_index = mag_get_thread_index(szone);
	magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);

	SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);

#if SMALL_CACHE
	ptr = (void *)small_mag_ptr->mag_last_free;

	if ((((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) == msize) {
		// we have a winner
		small_mag_ptr->mag_last_free = NULL;
		small_mag_ptr->mag_last_free_rgn = NULL;
		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
		CHECK(szone, __PRETTY_FUNCTION__);
		ptr = (void *)((uintptr_t)ptr & ~ (SMALL_QUANTUM - 1));
		if (cleared_requested) {
			memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
		}
		return ptr;
	}
#endif /* SMALL_CACHE */

	while(1) {
		ptr = small_malloc_from_free_list(szone, small_mag_ptr, mag_index, msize);
		if (ptr) {
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			CHECK(szone, __PRETTY_FUNCTION__);
			if (cleared_requested) {
				memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
			}
			return ptr;
		}

		if (small_get_region_from_depot(szone, small_mag_ptr, mag_index, msize)) {
			ptr = small_malloc_from_free_list(szone, small_mag_ptr, mag_index, msize);
			if (ptr) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				CHECK(szone, __PRETTY_FUNCTION__);
				if (cleared_requested) {
					memset(ptr, 0, SMALL_BYTES_FOR_MSIZE(msize));
				}
				return ptr;
			}
		}

		// The magazine is exhausted. A new region (heap) must be allocated to satisfy this call to malloc().
		// The allocation, an mmap() system call, will be performed outside the magazine spin locks by the first
		// thread that suffers the exhaustion. That thread sets "alloc_underway" and enters a critical section.
		// Threads arriving here later are excluded from the critical section, yield the CPU, and then retry the
		// allocation. After some time the magazine is resupplied, the original thread leaves with its allocation,
		// and retry-ing threads succeed in the code just above.
		if (!small_mag_ptr->alloc_underway) {
			void *fresh_region;

			// time to create a new region (do this outside the magazine lock)
			small_mag_ptr->alloc_underway = TRUE;
			OSMemoryBarrier();
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			fresh_region = allocate_pages_securely(szone, SMALL_REGION_SIZE, SMALL_BLOCKS_ALIGN, VM_MEMORY_MALLOC_SMALL);
			SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);

			MAGMALLOC_ALLOCREGION((void *)szone, (int)mag_index, fresh_region, SMALL_REGION_SIZE); // DTrace USDT Probe

			if (!fresh_region) { // out of memory!
				small_mag_ptr->alloc_underway = FALSE;
				OSMemoryBarrier();
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				return NULL;
			}

			ptr = small_malloc_from_region_no_lock(szone, small_mag_ptr, mag_index, msize, fresh_region);

			// we don't clear because this freshly allocated space is pristine
			small_mag_ptr->alloc_underway = FALSE;
			OSMemoryBarrier();
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			CHECK(szone, __PRETTY_FUNCTION__);
			return ptr;
		} else {
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			yield();
			SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
		}
	}
	/* NOTREACHED */
}

static NOINLINE void
free_small_botch(szone_t *szone, free_list_t *ptr)
{
	mag_index_t	mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
	magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);
	SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
	szone_error(szone, 1, "double free", ptr, NULL);
}

static INLINE void
free_small(szone_t *szone, void *ptr, region_t small_region, size_t known_size)
{
	msize_t	msize;
	mag_index_t	mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
	magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);

	// ptr is known to be in small_region
	if (known_size) {
		msize = SMALL_MSIZE_FOR_BYTES(known_size + SMALL_QUANTUM - 1);
	} else {
		msize = SMALL_PTR_SIZE(ptr);
		if (SMALL_PTR_IS_FREE(ptr)) {
			free_small_botch(szone, ptr);
			return;
		}
	}

	SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);

#if SMALL_CACHE
	// Depot does not participate in SMALL_CACHE since it can't be directly malloc()'d
	if (DEPOT_MAGAZINE_INDEX != mag_index) {

		void *ptr2 = small_mag_ptr->mag_last_free; // Might be NULL
		region_t rgn2 = small_mag_ptr->mag_last_free_rgn;

		/* check that we don't already have this pointer in the cache */
		if (ptr == (void *)((uintptr_t)ptr2 & ~ (SMALL_QUANTUM - 1))) {
			free_small_botch(szone, ptr);
			return;
		}

		if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && msize)
			memset(ptr, SCRABBLE_BYTE, SMALL_BYTES_FOR_MSIZE(msize));

		small_mag_ptr->mag_last_free = (void *)(((uintptr_t)ptr) | msize);
		small_mag_ptr->mag_last_free_rgn = small_region;

		if (!ptr2) {
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
			CHECK(szone, __PRETTY_FUNCTION__);
			return;
		}

		msize = (uintptr_t)ptr2 & (SMALL_QUANTUM - 1);
		ptr = (void *)(((uintptr_t)ptr2) & ~(SMALL_QUANTUM - 1));
		small_region = rgn2;
	}
#endif /* SMALL_CACHE */

	// Now in the time it took to acquire the lock, the region may have migrated
	// from one magazine to another. I.e. trailer->mag_index is volatile.
	// In which case the magazine lock we obtained (namely magazines[mag_index].mag_lock)
	// is stale. If so, keep on tryin' ...
	region_trailer_t *trailer = REGION_TRAILER_FOR_SMALL_REGION(small_region);
	mag_index_t refreshed_index;

	while (mag_index != (refreshed_index = trailer->mag_index)) { // Note assignment

		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);

		mag_index = refreshed_index;
		small_mag_ptr = &(szone->small_magazines[mag_index]);
		SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);
	}

	if (small_free_no_lock(szone, small_mag_ptr, mag_index, small_region, ptr, msize))
		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);

	CHECK(szone, __PRETTY_FUNCTION__);
}

static void
print_small_free_list(szone_t *szone)
{
	free_list_t		*ptr;
	_SIMPLE_STRING	b = _simple_salloc();
	mag_index_t mag_index;

	if (b) {
		_simple_sappend(b, "small free sizes:\n");
		for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
			grain_t	slot = 0;
			_simple_sprintf(b,"\tMagazine %d: ", mag_index);
			while (slot < szone->num_small_slots) {
				ptr = szone->small_magazines[mag_index].mag_free_list[slot];
				if (ptr) {
					_simple_sprintf(b, "%s%y[%d]; ", (slot == szone->num_small_slots-1) ? ">=" : "",
									(slot + 1) * SMALL_QUANTUM, free_list_count(szone, ptr));
				}
				slot++;
			}
			_simple_sappend(b,"\n");
		}
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
		_simple_sfree(b);
	}
}

static void
print_small_region(szone_t *szone, boolean_t verbose, region_t region, size_t bytes_at_start, size_t bytes_at_end)
{
	unsigned		counts[1024];
	unsigned		in_use = 0;
	uintptr_t		start = (uintptr_t)SMALL_REGION_ADDRESS(region);
	uintptr_t		current = start + bytes_at_start;
	uintptr_t		limit = (uintptr_t)SMALL_REGION_END(region) - bytes_at_end;
	msize_t		msize_and_free;
	msize_t		msize;
	unsigned		ci;
	_SIMPLE_STRING	b;
	uintptr_t		pgTot = 0;

	if (region == HASHRING_REGION_DEALLOCATED) {
		if ((b = _simple_salloc()) != NULL) {
			_simple_sprintf(b, "Small region [unknown address] was returned to the OS\n");
			_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
			_simple_sfree(b);
		}
		return;
	}

	memset(counts, 0, sizeof(counts));
	while (current < limit) {
		msize_and_free = *SMALL_METADATA_FOR_PTR(current);
		msize = msize_and_free & ~ SMALL_IS_FREE;
		if (!msize) {
			malloc_printf("*** error with %p: msize=%d\n", (void *)current, (unsigned)msize);
			break;
		}
		if (!(msize_and_free & SMALL_IS_FREE)) {
			// block in use
			if (msize < 1024)
				counts[msize]++;
			in_use++;
		} else {
			uintptr_t pgLo = round_page_quanta(current + sizeof(free_list_t) + sizeof(msize_t));
			uintptr_t pgHi = trunc_page_quanta(current + SMALL_BYTES_FOR_MSIZE(msize) - sizeof(msize_t));

			if (pgLo < pgHi) {
				pgTot += (pgHi - pgLo);
			}
		}
		current += SMALL_BYTES_FOR_MSIZE(msize);
	}
	if ((b = _simple_salloc()) != NULL) {
		_simple_sprintf(b, "Small region [%p-%p, %y] \t", (void *)start, SMALL_REGION_END(region), (int)SMALL_REGION_SIZE);
		_simple_sprintf(b, "Magazine=%d \t", MAGAZINE_INDEX_FOR_SMALL_REGION(region));
		_simple_sprintf(b, "Allocations in use=%d \t Bytes in use=%ly \t", in_use, BYTES_USED_FOR_SMALL_REGION(region));
		if (bytes_at_end || bytes_at_start)
			_simple_sprintf(b, "Untouched=%ly ", bytes_at_end + bytes_at_start);
		if (DEPOT_MAGAZINE_INDEX == MAGAZINE_INDEX_FOR_SMALL_REGION(region)) {
			_simple_sprintf(b, "Advised MADV_FREE=%ly", pgTot);
		} else {
			_simple_sprintf(b, "Fragments subject to reclamation=%ly", pgTot);
		}
		if (verbose && in_use) {
			_simple_sappend(b, "\n\tSizes in use: ");
			for (ci = 0; ci < 1024; ci++)
				if (counts[ci])
					_simple_sprintf(b, "%d[%d] ", SMALL_BYTES_FOR_MSIZE(ci), counts[ci]);
		}
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
		_simple_sfree(b);
	}
}

static boolean_t
small_free_list_check(szone_t *szone, grain_t slot)
{
	mag_index_t mag_index;

	for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
		magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);
		SZONE_MAGAZINE_PTR_LOCK(szone, small_mag_ptr);

		unsigned	count = 0;
		free_list_t	*ptr = szone->small_magazines[mag_index].mag_free_list[slot];
		msize_t		msize_and_free;
		free_list_t	*previous = NULL;

		while (ptr) {
			msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
			if (!(msize_and_free & SMALL_IS_FREE)) {
				malloc_printf("*** in-use ptr in free list slot=%d count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				return 0;
			}
			if (((uintptr_t)ptr) & (SMALL_QUANTUM - 1)) {
				malloc_printf("*** unaligned ptr in free list slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				return 0;
			}
			if (!small_region_for_ptr_no_lock(szone, ptr)) {
				malloc_printf("*** ptr not in szone slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				return 0;
			}
			if (free_list_unchecksum_ptr(szone, &ptr->previous) != previous) {
				malloc_printf("*** previous incorrectly set slot=%d  count=%d ptr=%p\n", slot, count, ptr);
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				return 0;
			}
			previous = ptr;
			ptr = free_list_unchecksum_ptr(szone, &ptr->next);
			count++;
		}

		SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
	}
	return 1;
}

/*******************************************************************************
 * Large allocator implementation
 ******************************************************************************/
#pragma mark large allocator

#if DEBUG_MALLOC

static void
large_debug_print(szone_t *szone)
{
	unsigned		index;
	large_entry_t	*range;
	_SIMPLE_STRING	b = _simple_salloc();

	if (b) {
		for (index = 0, range = szone->large_entries; index < szone->num_large_entries; index++, range++)
			if (range->address)
				_simple_sprintf(b, "%d: %p(%y);  ", index, range->address, range->size);

		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX, "%s\n", _simple_string(b));
		_simple_sfree(b);
	}
}
#endif

/*
 * Scan the hash ring looking for an entry for the given pointer.
 */
static large_entry_t *
large_entry_for_pointer_no_lock(szone_t *szone, const void *ptr)
{
	// result only valid with lock held
	unsigned		num_large_entries = szone->num_large_entries;
	unsigned		hash_index;
	unsigned		index;
	large_entry_t	*range;

	if (!num_large_entries)
		return NULL;

	hash_index = ((uintptr_t)ptr >> vm_page_quanta_shift) % num_large_entries;
	index = hash_index;

	do {
		range = szone->large_entries + index;
		if (range->address == (vm_address_t)ptr)
			return range;
		if (0 == range->address)
			return NULL; // end of chain
		index++;
		if (index == num_large_entries)
			index = 0;
	} while (index != hash_index);

	return NULL;
}

static void
large_entry_insert_no_lock(szone_t *szone, large_entry_t range)
{
	unsigned		num_large_entries = szone->num_large_entries;
	unsigned		hash_index = (((uintptr_t)(range.address)) >> vm_page_quanta_shift) % num_large_entries;
	unsigned		index = hash_index;
	large_entry_t	*entry;

	// assert(szone->num_large_objects_in_use < szone->num_large_entries); /* must be called with room to spare */

	do {
		entry = szone->large_entries + index;
		if (0 == entry->address) {
			*entry = range;
			return; // end of chain
		}
		index++;
		if (index == num_large_entries)
			index = 0;
	} while (index != hash_index);

	// assert(0); /* must not fallthrough! */
}

// FIXME: can't we simply swap the (now empty) entry with the last entry on the collision chain for this hash slot?
static INLINE void
large_entries_rehash_after_entry_no_lock(szone_t *szone, large_entry_t *entry)
{
	unsigned		num_large_entries = szone->num_large_entries;
	unsigned		hash_index = entry - szone->large_entries;
	unsigned		index = hash_index;
	large_entry_t	range;

	// assert(entry->address == 0) /* caller must have cleared *entry */

	do {
		index++;
		if (index == num_large_entries)
			index = 0;
		range = szone->large_entries[index];
		if (0 == range.address)
			return;
		szone->large_entries[index].address = (vm_address_t)0;
		szone->large_entries[index].size = 0;
		szone->large_entries[index].did_madvise_reusable = FALSE;
		large_entry_insert_no_lock(szone, range); // this will reinsert in the
		// proper place
	} while (index != hash_index);

	// assert(0); /* since entry->address == 0, must not fallthrough! */
}

// FIXME: num should probably be a size_t, since you can theoretically allocate
// more than 2^32-1 large_threshold objects in 64 bit.
static INLINE large_entry_t *
large_entries_alloc_no_lock(szone_t *szone, unsigned num)
{
	size_t	size = num * sizeof(large_entry_t);

	// Note that we allocate memory (via a system call) under a spin lock
	// That is certainly evil, however it's very rare in the lifetime of a process
	// The alternative would slow down the normal case
	return allocate_pages(szone, round_page_quanta(size), 0, 0, VM_MEMORY_MALLOC_LARGE);
}

static void
large_entries_free_no_lock(szone_t *szone, large_entry_t *entries, unsigned num, vm_range_t *range_to_deallocate)
{
	size_t	size = num * sizeof(large_entry_t);

	range_to_deallocate->address = (vm_address_t)entries;
	range_to_deallocate->size = round_page_quanta(size);
}

static large_entry_t *
large_entries_grow_no_lock(szone_t *szone, vm_range_t *range_to_deallocate)
{
	// sets range_to_deallocate
	unsigned		old_num_entries = szone->num_large_entries;
	large_entry_t	*old_entries = szone->large_entries;
	// always an odd number for good hashing
	unsigned		new_num_entries = (old_num_entries) ? old_num_entries * 2 + 1 :
	((vm_page_quanta_size / sizeof(large_entry_t)) - 1);
	large_entry_t	*new_entries = large_entries_alloc_no_lock(szone, new_num_entries);
	unsigned		index = old_num_entries;
	large_entry_t	oldRange;

	// if the allocation of new entries failed, bail
	if (new_entries == NULL)
		return NULL;

	szone->num_large_entries = new_num_entries;
	szone->large_entries = new_entries;

	/* rehash entries into the new list */
	while (index--) {
		oldRange = old_entries[index];
		if (oldRange.address) {
			large_entry_insert_no_lock(szone, oldRange);
		}
	}

	if (old_entries) {
		large_entries_free_no_lock(szone, old_entries, old_num_entries, range_to_deallocate);
	} else {
		range_to_deallocate->address = (vm_address_t)0;
		range_to_deallocate->size = 0;
	}

	return new_entries;
}

// frees the specific entry in the size table
// returns a range to truly deallocate
static vm_range_t
large_entry_free_no_lock(szone_t *szone, large_entry_t *entry)
{
	vm_range_t		range;

	range.address = entry->address;
	range.size = entry->size;

	if (szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) {
		protect((void *)range.address, range.size, PROT_READ | PROT_WRITE, szone->debug_flags);
		range.address -= vm_page_quanta_size;
		range.size += 2 * vm_page_quanta_size;
	}

	entry->address = 0;
	entry->size = 0;
	entry->did_madvise_reusable = FALSE;
	large_entries_rehash_after_entry_no_lock(szone, entry);

#if DEBUG_MALLOC
	if (large_entry_for_pointer_no_lock(szone, (void *)range.address)) {
		malloc_printf("*** freed entry %p still in use; num_large_entries=%d\n",
					  range.address, szone->num_large_entries);
		large_debug_print(szone);
		szone_sleep();
	}
#endif
	return range;
}

static NOINLINE kern_return_t
large_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t large_entries_address,
						unsigned num_entries, memory_reader_t reader, vm_range_recorder_t recorder)
{
	unsigned		index = 0;
	vm_range_t		buffer[MAX_RECORDER_BUFFER];
	unsigned		count = 0;
	large_entry_t	*entries;
	kern_return_t	err;
	vm_range_t		range;
	large_entry_t	entry;

	err = reader(task, large_entries_address, sizeof(large_entry_t) * num_entries, (void **)&entries);
	if (err)
		return err;

	index = num_entries;
	if (type_mask & MALLOC_ADMIN_REGION_RANGE_TYPE) {
		range.address = large_entries_address;
		range.size = round_page_quanta(num_entries * sizeof(large_entry_t));
		recorder(task, context, MALLOC_ADMIN_REGION_RANGE_TYPE, &range, 1);
	}
	if (type_mask & (MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE)) {
		while (index--) {
			entry = entries[index];
			if (entry.address) {
				range.address = entry.address;
				range.size = entry.size;
				buffer[count++] = range;
				if (count >= MAX_RECORDER_BUFFER) {
					recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE,
							 buffer, count);
					count = 0;
				}
			}
		}
	}
	if (count) {
		recorder(task, context, MALLOC_PTR_IN_USE_RANGE_TYPE | MALLOC_PTR_REGION_RANGE_TYPE,
				 buffer, count);
	}
	return 0;
}

static void *
large_malloc(szone_t *szone, size_t num_kernel_pages, unsigned char alignment,
			 boolean_t cleared_requested)
{
	void		*addr;
	vm_range_t		range_to_deallocate;
	size_t		size;
	large_entry_t	large_entry;

	if (!num_kernel_pages)
		num_kernel_pages = 1; // minimal allocation size for this szone
	size = (size_t)num_kernel_pages << vm_page_quanta_shift;
	range_to_deallocate.size = 0;
	range_to_deallocate.address = 0;

#if LARGE_CACHE
	if (size < LARGE_CACHE_SIZE_ENTRY_LIMIT) { // Look for a large_entry_t on the death-row cache?
		SZONE_LOCK(szone);

		int i, best = -1, idx = szone->large_entry_cache_newest, stop_idx = szone->large_entry_cache_oldest;
		size_t best_size = SIZE_T_MAX;

		while (1) { // Scan large_entry_cache for best fit, starting with most recent entry
			size_t this_size = szone->large_entry_cache[idx].size;
			addr = (void *)szone->large_entry_cache[idx].address;

			if (0 == alignment || 0 == (((uintptr_t) addr) & (((uintptr_t) 1 << alignment) - 1))) {
				if (size == this_size) { // size match!
					best = idx;
					best_size = this_size;
					break;
				}

				if (size <= this_size && this_size < best_size) { // improved fit?
					best = idx;
					best_size = this_size;
				}
			}

			if (idx == stop_idx) // exhausted live ring?
				break;

			if (idx)
				idx--; // bump idx down
			else
				idx = LARGE_ENTRY_CACHE_SIZE - 1; // wrap idx
		}

		if (best > -1 && (best_size - size) < size) { //limit fragmentation to 50%
			addr = (void *)szone->large_entry_cache[best].address;
			boolean_t was_madvised_reusable = szone->large_entry_cache[best].did_madvise_reusable;

			// Compact live ring to fill entry now vacated at large_entry_cache[best]
			// while preserving time-order
			if (szone->large_entry_cache_oldest < szone->large_entry_cache_newest) {

				// Ring hasn't wrapped. Fill in from right.
				for (i = best; i < szone->large_entry_cache_newest; ++i)
					szone->large_entry_cache[i] = szone->large_entry_cache[i + 1];

				szone->large_entry_cache_newest--; // Pull in right endpoint.

			} else if (szone->large_entry_cache_newest < szone->large_entry_cache_oldest) {

				// Ring has wrapped. Arrange to fill in from the contiguous side.
				if (best <= szone->large_entry_cache_newest) {
					// Fill from right.
					for (i = best; i < szone->large_entry_cache_newest; ++i)
						szone->large_entry_cache[i] = szone->large_entry_cache[i + 1];

					if (0 < szone->large_entry_cache_newest)
						szone->large_entry_cache_newest--;
					else
						szone->large_entry_cache_newest = LARGE_ENTRY_CACHE_SIZE - 1;
				} else {
					// Fill from left.
					for ( i = best; i > szone->large_entry_cache_oldest; --i)
						szone->large_entry_cache[i] = szone->large_entry_cache[i - 1];

					if (szone->large_entry_cache_oldest < LARGE_ENTRY_CACHE_SIZE - 1)
						szone->large_entry_cache_oldest++;
					else
						szone->large_entry_cache_oldest = 0;
				}

			} else {
				// By trichotomy, large_entry_cache_newest == large_entry_cache_oldest.
				// That implies best == large_entry_cache_newest == large_entry_cache_oldest
				// and the ring is now empty.
				szone->large_entry_cache[best].address = 0;
				szone->large_entry_cache[best].size = 0;
				szone->large_entry_cache[best].did_madvise_reusable = FALSE;
			}

			if ((szone->num_large_objects_in_use + 1) * 4 > szone->num_large_entries) {
				// density of hash table too high; grow table
				// we do that under lock to avoid a race
				large_entry_t *entries = large_entries_grow_no_lock(szone, &range_to_deallocate);
				if (entries == NULL) {
					SZONE_UNLOCK(szone);
					return NULL;
				}
			}

			large_entry.address = (vm_address_t)addr;
			large_entry.size = best_size;
			large_entry.did_madvise_reusable = FALSE;
			large_entry_insert_no_lock(szone, large_entry);

			szone->num_large_objects_in_use ++;
			szone->num_bytes_in_large_objects += best_size;
			if (!was_madvised_reusable)
				szone->large_entry_cache_reserve_bytes -= best_size;

			szone->large_entry_cache_bytes -= best_size;

			if (szone->flotsam_enabled && szone->large_entry_cache_bytes < SZONE_FLOTSAM_THRESHOLD_LOW) {
				szone->flotsam_enabled = FALSE;
			}

			SZONE_UNLOCK(szone);

			if (range_to_deallocate.size) {
				// we deallocate outside the lock
				deallocate_pages(szone, (void *)range_to_deallocate.address, range_to_deallocate.size, 0);
			}

			// Perform the madvise() outside the lock.
			// Typically the madvise() is successful and we'll quickly return from this routine.
			// In the unusual case of failure, reacquire the lock to unwind.
#if TARGET_OS_EMBEDDED
			// Ok to do this madvise on embedded because we won't call MADV_FREE_REUSABLE on a large
			// cache block twice without MADV_FREE_REUSE in between.
#endif
			if (was_madvised_reusable && -1 == madvise(addr, size, MADV_FREE_REUSE)) {
				/* -1 return: VM map entry change makes this unfit for reuse. */
#if DEBUG_MADVISE
				szone_error(szone, 0, "large_malloc madvise(..., MADV_FREE_REUSE) failed",
							addr, "length=%d\n", size);
#endif

				SZONE_LOCK(szone);
				szone->num_large_objects_in_use--;
				szone->num_bytes_in_large_objects -= large_entry.size;

				// Re-acquire "entry" after interval just above where we let go the lock.
				large_entry_t *entry = large_entry_for_pointer_no_lock(szone, addr);
				if (NULL == entry) {
					szone_error(szone, 1, "entry for pointer being discarded from death-row vanished", addr, NULL);
					SZONE_UNLOCK(szone);
				} else {

					range_to_deallocate = large_entry_free_no_lock(szone, entry);
					SZONE_UNLOCK(szone);

					if (range_to_deallocate.size) {
						// we deallocate outside the lock
						deallocate_pages(szone, (void *)range_to_deallocate.address, range_to_deallocate.size, 0);
					}
				}
				/* Fall through to allocate_pages() afresh. */
			} else {
				if (cleared_requested) {
					memset(addr, 0, size);
				}

				return addr;
			}
		} else {
			SZONE_UNLOCK(szone);
		}
	}

	range_to_deallocate.size = 0;
	range_to_deallocate.address = 0;
#endif /* LARGE_CACHE */

	addr = allocate_pages(szone, size, alignment, szone->debug_flags, VM_MEMORY_MALLOC_LARGE);
	if (addr == NULL) {
		return NULL;
	}

	SZONE_LOCK(szone);
	if ((szone->num_large_objects_in_use + 1) * 4 > szone->num_large_entries) {
		// density of hash table too high; grow table
		// we do that under lock to avoid a race
		large_entry_t *entries = large_entries_grow_no_lock(szone, &range_to_deallocate);
		if (entries == NULL) {
			SZONE_UNLOCK(szone);
			return NULL;
		}
	}

	large_entry.address = (vm_address_t)addr;
	large_entry.size = size;
	large_entry.did_madvise_reusable = FALSE;
	large_entry_insert_no_lock(szone, large_entry);

	szone->num_large_objects_in_use ++;
	szone->num_bytes_in_large_objects += size;
	SZONE_UNLOCK(szone);

	if (range_to_deallocate.size) {
		// we deallocate outside the lock
		deallocate_pages(szone, (void *)range_to_deallocate.address, range_to_deallocate.size, 0);
	}
	return addr;
}

static NOINLINE void
free_large(szone_t *szone, void *ptr)
{
	// We have established ptr is page-aligned and neither tiny nor small
	large_entry_t	*entry;
	vm_range_t		vm_range_to_deallocate;

	SZONE_LOCK(szone);
	entry = large_entry_for_pointer_no_lock(szone, ptr);
	if (entry) {
#if LARGE_CACHE
		if (entry->size < LARGE_CACHE_SIZE_ENTRY_LIMIT &&
			-1 != madvise((void *)(entry->address), entry->size, MADV_CAN_REUSE)) { // Put the large_entry_t on the death-row cache?
			int idx = szone->large_entry_cache_newest, stop_idx = szone->large_entry_cache_oldest;
			large_entry_t this_entry = *entry; // Make a local copy, "entry" is volatile when lock is let go.
			boolean_t reusable = TRUE;
			boolean_t should_madvise = szone->large_entry_cache_reserve_bytes + this_entry.size > szone->large_entry_cache_reserve_limit;

			// Already freed?
			// [Note that repeated entries in death-row risk vending the same entry subsequently
			// to two different malloc() calls. By checking here the (illegal) double free
			// is accommodated, matching the behavior of the previous implementation.]
			while (1) { // Scan large_entry_cache starting with most recent entry
				if (szone->large_entry_cache[idx].address == entry->address) {
					szone_error(szone, 1, "pointer being freed already on death-row", ptr, NULL);
					SZONE_UNLOCK(szone);
					return;
				}

				if (idx == stop_idx) // exhausted live ring?
					break;

				if (idx)
					idx--; // bump idx down
				else
					idx = LARGE_ENTRY_CACHE_SIZE - 1; // wrap idx
			}

			SZONE_UNLOCK(szone);

			if (szone->debug_flags & SCALABLE_MALLOC_PURGEABLE) { // Are we a purgable zone?
				int state = VM_PURGABLE_NONVOLATILE; // restore to default condition

				if (KERN_SUCCESS != vm_purgable_control(mach_task_self(), this_entry.address, VM_PURGABLE_SET_STATE, &state)) {
					malloc_printf("*** can't vm_purgable_control(..., VM_PURGABLE_SET_STATE) for large freed block at %p\n",
								  this_entry.address);
					reusable = FALSE;
				}
			}

			if (szone->large_legacy_reset_mprotect) { // Linked for Leopard?
				// Accomodate Leopard apps that (illegally) mprotect() their own guard pages on large malloc'd allocations
				int err = mprotect((void *)(this_entry.address), this_entry.size, PROT_READ | PROT_WRITE);
				if (err) {
					malloc_printf("*** can't reset protection for large freed block at %p\n", this_entry.address);
					reusable = FALSE;
				}
			}

			// madvise(..., MADV_REUSABLE) death-row arrivals if hoarding would exceed large_entry_cache_reserve_limit
			if (should_madvise) {
				// Issue madvise to avoid paging out the dirtied free()'d pages in "entry"
				MAGMALLOC_MADVFREEREGION((void *)szone, (void *)0, (void *)(this_entry.address), this_entry.size); // DTrace USDT Probe

#if TARGET_OS_EMBEDDED
				// Ok to do this madvise on embedded because we won't call MADV_FREE_REUSABLE on a large
				// cache block twice without MADV_FREE_REUSE in between.
#endif
				if (-1 == madvise((void *)(this_entry.address), this_entry.size, MADV_FREE_REUSABLE)) {
					/* -1 return: VM map entry change makes this unfit for reuse. */
#if DEBUG_MADVISE
					szone_error(szone, 0, "free_large madvise(..., MADV_FREE_REUSABLE) failed",
								(void *)this_entry.address, "length=%d\n", this_entry.size);
#endif
					reusable = FALSE;
				}
			}

			SZONE_LOCK(szone);

			// Re-acquire "entry" after interval just above where we let go the lock.
			entry = large_entry_for_pointer_no_lock(szone, ptr);
			if (NULL == entry) {
				szone_error(szone, 1, "entry for pointer being freed from death-row vanished", ptr, NULL);
				SZONE_UNLOCK(szone);
				return;
			}

			// Add "entry" to death-row ring
			if (reusable) {
				int idx = szone->large_entry_cache_newest; // Most recently occupied
				vm_address_t addr;
				size_t adjsize;

				if (szone->large_entry_cache_newest == szone->large_entry_cache_oldest &&
					0 == szone->large_entry_cache[idx].address) {
					// Ring is empty, idx is good as it stands
					addr = 0;
					adjsize = 0;
				} else {
					// Extend the queue to the "right" by bumping up large_entry_cache_newest
					if (idx == LARGE_ENTRY_CACHE_SIZE - 1)
						idx = 0; // Wrap index
					else
						idx++; // Bump index

					if (idx == szone->large_entry_cache_oldest) { // Fully occupied
						// Drop this entry from the cache and deallocate the VM
						addr = szone->large_entry_cache[idx].address;
						adjsize = szone->large_entry_cache[idx].size;
						szone->large_entry_cache_bytes -= adjsize;
						if (!szone->large_entry_cache[idx].did_madvise_reusable)
							szone->large_entry_cache_reserve_bytes -= adjsize;
					} else {
						// Using an unoccupied cache slot
						addr = 0;
						adjsize = 0;
					}
				}

				if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE))
					memset((void *)(entry->address), should_madvise ? SCRUBBLE_BYTE : SCRABBLE_BYTE, entry->size);

				entry->did_madvise_reusable = should_madvise; // Was madvise()'d above?
				if (!should_madvise) // Entered on death-row without madvise() => up the hoard total
					szone->large_entry_cache_reserve_bytes += entry->size;

				szone->large_entry_cache_bytes += entry->size;

				if (!szone->flotsam_enabled && szone->large_entry_cache_bytes > SZONE_FLOTSAM_THRESHOLD_HIGH) {
					szone->flotsam_enabled = TRUE;
				}

				szone->large_entry_cache[idx] = *entry;
				szone->large_entry_cache_newest = idx;

				szone->num_large_objects_in_use--;
				szone->num_bytes_in_large_objects -= entry->size;

				(void)large_entry_free_no_lock(szone, entry);

				if (0 == addr) {
					SZONE_UNLOCK(szone);
					return;
				}

				// Fall through to drop large_entry_cache_oldest from the cache,
				// and then deallocate its pages.

				// Trim the queue on the "left" by bumping up large_entry_cache_oldest
				if (szone->large_entry_cache_oldest == LARGE_ENTRY_CACHE_SIZE - 1)
					szone->large_entry_cache_oldest = 0;
				else
					szone->large_entry_cache_oldest++;

				// we deallocate_pages, including guard pages, outside the lock
				SZONE_UNLOCK(szone);
				deallocate_pages(szone, (void *)addr, (size_t)adjsize, 0);
				return;
			} else {
				/* fall through to discard an allocation that is not reusable */
			}
		}
#endif /* LARGE_CACHE */

		szone->num_large_objects_in_use--;
		szone->num_bytes_in_large_objects -= entry->size;

		vm_range_to_deallocate = large_entry_free_no_lock(szone, entry);
	} else {
#if DEBUG_MALLOC
		large_debug_print(szone);
#endif
		szone_error(szone, 1, "pointer being freed was not allocated", ptr, NULL);
		SZONE_UNLOCK(szone);
		return;
	}
	SZONE_UNLOCK(szone); // we release the lock asap
	CHECK(szone, __PRETTY_FUNCTION__);

	// we deallocate_pages, including guard pages, outside the lock
	if (vm_range_to_deallocate.address) {
#if DEBUG_MALLOC
		// FIXME: large_entry_for_pointer_no_lock() needs the lock held ...
		if (large_entry_for_pointer_no_lock(szone, (void *)vm_range_to_deallocate.address)) {
			malloc_printf("*** invariant broken: %p still in use num_large_entries=%d\n",
						  vm_range_to_deallocate.address, szone->num_large_entries);
			large_debug_print(szone);
			szone_sleep();
		}
#endif
		deallocate_pages(szone, (void *)vm_range_to_deallocate.address, (size_t)vm_range_to_deallocate.size, 0);
	}
}

static INLINE void *
large_try_shrink_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_good_size)
{
	size_t shrinkage = old_size - new_good_size;

	if (shrinkage) {
		SZONE_LOCK(szone);
		/* contract existing large entry */
		large_entry_t *large_entry = large_entry_for_pointer_no_lock(szone, ptr);
		if (!large_entry) {
			szone_error(szone, 1, "large entry reallocated is not properly in table", ptr, NULL);
			SZONE_UNLOCK(szone);
			return ptr;
		}

		large_entry->address = (vm_address_t)ptr;
		large_entry->size = new_good_size;
		szone->num_bytes_in_large_objects -= shrinkage;
		SZONE_UNLOCK(szone); // we release the lock asap

		deallocate_pages(szone, (void *)((uintptr_t)ptr + new_good_size), shrinkage, 0);
	}
	return ptr;
}

static INLINE int
large_try_realloc_in_place(szone_t *szone, void *ptr, size_t old_size, size_t new_size)
{
	vm_address_t	addr = (vm_address_t)ptr + old_size;
	large_entry_t	*large_entry;
	kern_return_t	err;

	SZONE_LOCK(szone);
	large_entry = large_entry_for_pointer_no_lock(szone, (void *)addr);
	SZONE_UNLOCK(szone);

	if (large_entry) { // check if "addr = ptr + old_size" is already spoken for
		return 0; // large pointer already exists in table - extension is not going to work
	}

	new_size = round_page_quanta(new_size);
	/*
	 * Ask for allocation at a specific address, and mark as realloc
	 * to request coalescing with previous realloc'ed extensions.
	 */
	err = vm_allocate(mach_task_self(), &addr, new_size - old_size, VM_MAKE_TAG(VM_MEMORY_REALLOC));
	if (err != KERN_SUCCESS) {
		return 0;
	}

	SZONE_LOCK(szone);
	/* extend existing large entry */
	large_entry = large_entry_for_pointer_no_lock(szone, ptr);
	if (!large_entry) {
		szone_error(szone, 1, "large entry reallocated is not properly in table", ptr, NULL);
		SZONE_UNLOCK(szone);
		return 0; // Bail, leaking "addr"
	}

	large_entry->address = (vm_address_t)ptr;
	large_entry->size = new_size;
	szone->num_bytes_in_large_objects += new_size - old_size;
	SZONE_UNLOCK(szone); // we release the lock asap

	return 1;
}

/*********************	Zone call backs	************************/
/*
 * Mark these NOINLINE to avoid bloating the purgeable zone call backs
 */
static NOINLINE void
szone_free(szone_t *szone, void *ptr)
{
	region_t	tiny_region;
	region_t	small_region;

#if DEBUG_MALLOC
	if (LOG(szone, ptr))
		malloc_printf("in szone_free with %p\n", ptr);
#endif
	if (!ptr)
		return;
	/*
	 * Try to free to a tiny region.
	 */
	if ((uintptr_t)ptr & (TINY_QUANTUM - 1)) {
		szone_error(szone, 1, "Non-aligned pointer being freed", ptr, NULL);
		return;
	}
	if ((tiny_region = tiny_region_for_ptr_no_lock(szone, ptr)) != NULL) {
		if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS) {
			szone_error(szone, 1, "Pointer to metadata being freed", ptr, NULL);
			return;
		}
		free_tiny(szone, ptr, tiny_region, 0);
		return;
	}

	/*
	 * Try to free to a small region.
	 */
	if ((uintptr_t)ptr & (SMALL_QUANTUM - 1)) {
		szone_error(szone, 1, "Non-aligned pointer being freed (2)", ptr, NULL);
		return;
	}
	if ((small_region = small_region_for_ptr_no_lock(szone, ptr)) != NULL) {
		if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS) {
			szone_error(szone, 1, "Pointer to metadata being freed (2)", ptr, NULL);
			return;
		}
		free_small(szone, ptr, small_region, 0);
		return;
	}

	/* check that it's a legal large allocation */
	if ((uintptr_t)ptr & (vm_page_quanta_size - 1)) {
		szone_error(szone, 1, "non-page-aligned, non-allocated pointer being freed", ptr, NULL);
		return;
	}
	free_large(szone, ptr);
}

static NOINLINE void
szone_free_definite_size(szone_t *szone, void *ptr, size_t size)
{
#if DEBUG_MALLOC
	if (LOG(szone, ptr))
		malloc_printf("in szone_free_definite_size with %p\n", ptr);

	if (0 == size) {
		szone_error(szone, 1, "pointer of size zero being freed", ptr, NULL);
		return;
	}

#endif
	if (!ptr)
		return;

	/*
	 * Try to free to a tiny region.
	 */
	if ((uintptr_t)ptr & (TINY_QUANTUM - 1)) {
		szone_error(szone, 1, "Non-aligned pointer being freed", ptr, NULL);
		return;
	}
	if (size <= (NUM_TINY_SLOTS - 1)*TINY_QUANTUM) {
		if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS) {
			szone_error(szone, 1, "Pointer to metadata being freed", ptr, NULL);
			return;
		}
		free_tiny(szone, ptr, TINY_REGION_FOR_PTR(ptr), size);
		return;
	}

	/*
	 * Try to free to a small region.
	 */
	if ((uintptr_t)ptr & (SMALL_QUANTUM - 1)) {
		szone_error(szone, 1, "Non-aligned pointer being freed (2)", ptr, NULL);
		return;
	}
	if (size <= szone->large_threshold) {
		if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS) {
			szone_error(szone, 1, "Pointer to metadata being freed (2)", ptr, NULL);
			return;
		}
		free_small(szone, ptr, SMALL_REGION_FOR_PTR(ptr), size);
		return;
	}

	/* check that it's a legal large allocation */
	if ((uintptr_t)ptr & (vm_page_quanta_size - 1)) {
		szone_error(szone, 1, "non-page-aligned, non-allocated pointer being freed", ptr, NULL);
		return;
	}
	free_large(szone, ptr);
}

static NOINLINE void *
szone_malloc_should_clear(szone_t *szone, size_t size, boolean_t cleared_requested)
{
	void	*ptr;
	msize_t	msize;

	if (size <= (NUM_TINY_SLOTS - 1)*TINY_QUANTUM) {
		// think tiny
		msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
		if (!msize)
			msize = 1;
		ptr = tiny_malloc_should_clear(szone, msize, cleared_requested);
	} else if (size <= szone->large_threshold) {
		// think small
		msize = SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1);
		if (!msize)
			msize = 1;
		ptr = small_malloc_should_clear(szone, msize, cleared_requested);
	} else {
		// large
		size_t num_kernel_pages = round_page_quanta(size) >> vm_page_quanta_shift;
		if (num_kernel_pages == 0)	/* Overflowed */
			ptr = 0;
		else
			ptr = large_malloc(szone, num_kernel_pages, 0, cleared_requested);
	}
#if DEBUG_MALLOC
	if (LOG(szone, ptr))
		malloc_printf("szone_malloc returned %p\n", ptr);
#endif
	/*
	 * If requested, scribble on allocated memory.
	 */
	if ((szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE) && ptr && !cleared_requested && size)
		memset(ptr, SCRIBBLE_BYTE, szone_size(szone, ptr));

	return ptr;
}

static NOINLINE void *
szone_malloc(szone_t *szone, size_t size) {
	return szone_malloc_should_clear(szone, size, 0);
}

static NOINLINE void *
szone_calloc(szone_t *szone, size_t num_items, size_t size)
{
	size_t total_bytes = num_items * size;

	// Check for overflow of integer multiplication
	if (num_items > 1) {
#if __LP64__ /* size_t is uint64_t */
		if ((num_items | size) & 0xffffffff00000000ul) {
			// num_items or size equals or exceeds sqrt(2^64) == 2^32, appeal to wider arithmetic
			__uint128_t product = ((__uint128_t)num_items) * ((__uint128_t)size);
			if ((uint64_t)(product >> 64)) // compiles to test on upper register of register pair
				return NULL;
		}
#else /* size_t is uint32_t */
		if ((num_items | size) & 0xffff0000ul) {
			// num_items or size equals or exceeds sqrt(2^32) == 2^16, appeal to wider arithmetic
			uint64_t product = ((uint64_t)num_items) * ((uint64_t)size);
			if ((uint32_t)(product >> 32)) // compiles to test on upper register of register pair
				return NULL;
		}
#endif
	}

	return szone_malloc_should_clear(szone, total_bytes, 1);
}

static NOINLINE void *
szone_valloc(szone_t *szone, size_t size)
{
	void	*ptr;

	if (size <= szone->large_threshold) {
		ptr = szone_memalign(szone, vm_page_quanta_size, size);
	} else {
		size_t	num_kernel_pages;

		num_kernel_pages = round_page_quanta(size) >> vm_page_quanta_shift;
		ptr = large_malloc(szone, num_kernel_pages, 0, 0);
	}

#if DEBUG_MALLOC
	if (LOG(szone, ptr))
		malloc_printf("szone_valloc returned %p\n", ptr);
#endif
	return ptr;
}

/* Isolate PIC-base load here. */
static NOINLINE size_t
szone_size_try_large(szone_t *szone, const void *ptr)
{
	size_t		size = 0;
	large_entry_t	*entry;

	SZONE_LOCK(szone);
	entry = large_entry_for_pointer_no_lock(szone, ptr);
	if (entry) {
		size = entry->size;
	}
	SZONE_UNLOCK(szone);
#if DEBUG_MALLOC
	if (LOG(szone, ptr)) {
		malloc_printf("szone_size for %p returned %d\n", ptr, (unsigned)size);
	}
#endif
	return size;
}

static NOINLINE size_t
szone_size(szone_t *szone, const void *ptr)
{
	boolean_t		is_free;
	msize_t		msize, msize_and_free;

	if (!ptr)
		return 0;
#if DEBUG_MALLOC
	if (LOG(szone, ptr)) {
		malloc_printf("in szone_size for %p (szone=%p)\n", ptr, szone);
	}
#endif

	/*
	 * Look for it in a tiny region.
	 */
	if ((uintptr_t)ptr & (TINY_QUANTUM - 1))
		return 0;
	if (tiny_region_for_ptr_no_lock(szone, ptr)) {
		if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS)
			return 0;
		msize = get_tiny_meta_header(ptr, &is_free);
		if (is_free)
			return 0;
#if TINY_CACHE
		{
			mag_index_t mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(ptr));
			if (DEPOT_MAGAZINE_INDEX != mag_index) {
				magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

				if (msize < TINY_QUANTUM && ptr == (void *)((uintptr_t)(tiny_mag_ptr->mag_last_free) & ~ (TINY_QUANTUM - 1)))
					return 0;
			} else {
				for (mag_index = 0; mag_index < szone->num_tiny_magazines; mag_index++) {
					magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

					if (msize < TINY_QUANTUM && ptr == (void *)((uintptr_t)(tiny_mag_ptr->mag_last_free) & ~ (TINY_QUANTUM - 1)))
						return 0;
				}
			}
		}
#endif
		return TINY_BYTES_FOR_MSIZE(msize);
	}

	/*
	 * Look for it in a small region.
	 */
	if ((uintptr_t)ptr & (SMALL_QUANTUM - 1))
		return 0;
	if (small_region_for_ptr_no_lock(szone, ptr)) {
		if (SMALL_META_INDEX_FOR_PTR(ptr) >= NUM_SMALL_BLOCKS)
			return 0;
		msize_and_free = *SMALL_METADATA_FOR_PTR(ptr);
		if (msize_and_free & SMALL_IS_FREE)
			return 0;
#if SMALL_CACHE
		{
			mag_index_t	mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(ptr));
			if (DEPOT_MAGAZINE_INDEX != mag_index) {
				magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);

				if (ptr == (void *)((uintptr_t)(small_mag_ptr->mag_last_free) & ~ (SMALL_QUANTUM - 1)))
					return 0;
			} else {
				for (mag_index = 0; mag_index < szone->num_small_magazines; mag_index++) {
					magazine_t	*small_mag_ptr = &(szone->small_magazines[mag_index]);

					if (ptr == (void *)((uintptr_t)(small_mag_ptr->mag_last_free) & ~ (SMALL_QUANTUM - 1)))
						return 0;
				}
			}
		}
#endif
		return SMALL_BYTES_FOR_MSIZE(msize_and_free);
	}

	/*
	 * If not page-aligned, it cannot have come from a large allocation.
	 */
	if ((uintptr_t)ptr & (vm_page_quanta_size - 1))
		return 0;

	/*
	 * Look for it in a large entry.
	 */
	return szone_size_try_large(szone, ptr);
}

static NOINLINE void *
szone_realloc(szone_t *szone, void *ptr, size_t new_size)
{
	size_t	old_size, new_good_size, valid_size;
	void	*new_ptr;

#if DEBUG_MALLOC
	if (LOG(szone, ptr)) {
		malloc_printf("in szone_realloc for %p, %d\n", ptr, (unsigned)new_size);
	}
#endif
	if (NULL == ptr) {
		// If ptr is a null pointer, realloc() shall be equivalent to malloc() for the specified size.
		return szone_malloc(szone, new_size);
	} else if (0 == new_size) {
		// If size is 0 and ptr is not a null pointer, the object pointed to is freed.
		szone_free(szone, ptr);
		// If size is 0, either a null pointer or a unique pointer that can be successfully passed
		// to free() shall be returned.
		return szone_malloc(szone, 1);
	}

	old_size = szone_size(szone, ptr);
	if (!old_size) {
		szone_error(szone, 1, "pointer being reallocated was not allocated", ptr, NULL);
		return NULL;
	}

	new_good_size = szone_good_size(szone, new_size);
	if (new_good_size == old_size) { // Existing allocation is best fit evar?
		return ptr;
	}

	/*
	 * If the new size suits the tiny allocator and the pointer being resized
	 * belongs to a tiny region, try to reallocate in-place.
	 */
	if (new_good_size <= (NUM_TINY_SLOTS - 1) * TINY_QUANTUM) {
		if (old_size <= (NUM_TINY_SLOTS - 1) * TINY_QUANTUM) {
			if (new_good_size <= (old_size >> 1)) {
				/*
				 * Serious shrinkage (more than half). free() the excess.
				 */
				return tiny_try_shrink_in_place(szone, ptr, old_size, new_good_size);
			} else if (new_good_size <= old_size) {
				/*
				 * new_good_size smaller than old_size but not by much (less than half).
				 * Avoid thrashing at the expense of some wasted storage.
				 */
				if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
					memset(ptr + new_size, SCRIBBLE_BYTE, old_size - new_size);
				return ptr;
			} else if (tiny_try_realloc_in_place(szone, ptr, old_size, new_good_size)) { // try to grow the allocation
				if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
					memset(ptr + old_size, SCRIBBLE_BYTE, new_good_size - old_size);
				return ptr;
			}
		}

		/*
		 * Else if the new size suits the small allocator and the pointer being resized
		 * belongs to a small region, and we're not protecting the small allocations
		 * try to reallocate in-place.
		 */
	} else if (new_good_size <= szone->large_threshold) {
		if ((NUM_TINY_SLOTS - 1) * TINY_QUANTUM < old_size && old_size <= szone->large_threshold) {
			if (new_good_size <= (old_size >> 1)) {
				return small_try_shrink_in_place(szone, ptr, old_size, new_good_size);
			} else if (new_good_size <= old_size) {
				if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
					memset(ptr + new_size, SCRIBBLE_BYTE, old_size - new_size);
				return ptr;
			} else if (small_try_realloc_in_place(szone, ptr, old_size, new_good_size)) {
				if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
					memset(ptr + old_size, SCRIBBLE_BYTE, new_good_size - old_size);
				return ptr;
			}
		}
		/*
		 * Else if the allocation's a large allocation, try to reallocate in-place there.
		 */
	} else if (!(szone->debug_flags & SCALABLE_MALLOC_PURGEABLE) && // purgeable needs fresh allocation
			   (old_size > szone->large_threshold) &&
			   (new_good_size > szone->large_threshold)) {
		if (new_good_size <= (old_size >> 1)) {
			return large_try_shrink_in_place(szone, ptr, old_size, new_good_size);
		} else if (new_good_size <= old_size) {
			if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
				memset(ptr + new_size, SCRIBBLE_BYTE, old_size - new_size);
			return ptr;
		} else if (large_try_realloc_in_place(szone, ptr, old_size, new_good_size)) {
			if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
				memset(ptr + old_size, SCRIBBLE_BYTE, new_good_size - old_size);
			return ptr;
		}
	}

	/*
	 * Can't reallocate in place for whatever reason; allocate a new buffer and copy.
	 */
	if (new_good_size <= (old_size >> 1)) {
		/* Serious shrinkage (more than half). FALL THROUGH to alloc/copy/free. */
	} else if (new_good_size <= old_size) {
		if (szone->debug_flags & SCALABLE_MALLOC_DO_SCRIBBLE)
			memset(ptr + new_size, SCRIBBLE_BYTE, old_size - new_size);
		return ptr;
	}

	new_ptr = szone_malloc(szone, new_size);
	if (new_ptr == NULL)
		return NULL;

	/*
	 * If the allocation's large enough, try to copy using VM.  If that fails, or
	 * if it's too small, just copy by hand.
	 */
	valid_size = MIN(old_size, new_size);
	if ((valid_size < szone->vm_copy_threshold) ||
		vm_copy(mach_task_self(), (vm_address_t)ptr, valid_size, (vm_address_t)new_ptr))
		memcpy(new_ptr, ptr, valid_size);
	szone_free(szone, ptr);

#if DEBUG_MALLOC
	if (LOG(szone, ptr)) {
		malloc_printf("szone_realloc returned %p for %d\n", new_ptr, (unsigned)new_size);
	}
#endif
	return new_ptr;
}

static NOINLINE void *
szone_memalign(szone_t *szone, size_t alignment, size_t size)
{
	if (size == 0)
		size = 1; // Ensures we'll return an aligned free()-able pointer

	if ((size + alignment) < size) // size_t arithmetic wrapped!
		return NULL;

	// alignment is gauranteed a power of 2 at least as large as sizeof(void *), hence non-zero.
	// Since size + alignment didn't wrap, 0 <= size + alignment - 1 < size + alignment
	size_t span = size + alignment - 1;

	if (alignment <= TINY_QUANTUM) {
		return szone_malloc(szone, size); // Trivially satisfied by tiny, small, or large

	} else if (span <= (NUM_TINY_SLOTS - 1)*TINY_QUANTUM) {
		msize_t mspan = TINY_MSIZE_FOR_BYTES(span + TINY_QUANTUM - 1);
		void *p = szone_malloc(szone, span); // avoids inlining tiny_malloc_should_clear(szone, mspan, 0);

		if (NULL == p)
			return NULL;

		size_t offset = ((uintptr_t) p) & (alignment - 1); // p % alignment
		size_t pad = (0 == offset) ? 0 : alignment - offset; // p + pad achieves desired alignment

		msize_t msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
		msize_t mpad = TINY_MSIZE_FOR_BYTES(pad + TINY_QUANTUM - 1);
		msize_t mwaste = mspan - msize - mpad; // excess blocks

		if (mpad > 0) {
			void *q = (void *)(((uintptr_t) p) + pad);

			// Mark q as a block header and in-use, thus creating two blocks.
			magazine_t	*tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																		 REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(p)),
																		 MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(p)));
			set_tiny_meta_header_in_use(q, msize);
			tiny_mag_ptr->mag_num_objects++;

			// set_tiny_meta_header_in_use() "reaffirms" the block_header on the *following* block, so
			// now set its in_use bit as well. But only if its within the original allocation made above.
			if (mwaste > 0)
				BITARRAY_SET(TINY_INUSE_FOR_HEADER(TINY_BLOCK_HEADER_FOR_PTR(q)), TINY_INDEX_FOR_PTR(q) + msize);
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);

			// Give up mpad blocks beginning at p to the tiny free list
			// region_t r = TINY_REGION_FOR_PTR(p);
			szone_free(szone, p); // avoids inlining free_tiny(szone, p, &r);

			p = q; // advance p to the desired alignment
		}

		if (mwaste > 0) {
			void *q = (void *)(((uintptr_t) p) + TINY_BYTES_FOR_MSIZE(msize));
			// Mark q as block header and in-use, thus creating two blocks.
			magazine_t	*tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																		 REGION_TRAILER_FOR_TINY_REGION(TINY_REGION_FOR_PTR(p)),
																		 MAGAZINE_INDEX_FOR_TINY_REGION(TINY_REGION_FOR_PTR(p)));
			set_tiny_meta_header_in_use(q, mwaste);
			tiny_mag_ptr->mag_num_objects++;
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);

			// Give up mwaste blocks beginning at q to the tiny free list
			// region_t r = TINY_REGION_FOR_PTR(q);
			szone_free(szone, q); // avoids inlining free_tiny(szone, q, &r);
		}

		return p; // p has the desired size and alignment, and can later be free()'d

	} else if ((NUM_TINY_SLOTS - 1)*TINY_QUANTUM < size && alignment <= SMALL_QUANTUM) {
		return szone_malloc(szone, size); // Trivially satisfied by small or large

	} else if (span <= szone->large_threshold) {

		if (size <= (NUM_TINY_SLOTS - 1)*TINY_QUANTUM) {
			size = (NUM_TINY_SLOTS - 1)*TINY_QUANTUM + TINY_QUANTUM; // ensure block allocated by small does not have a tiny-possible size
			span = size + alignment - 1;
		}

		msize_t mspan = SMALL_MSIZE_FOR_BYTES(span + SMALL_QUANTUM - 1);
		void *p = szone_malloc(szone, span); // avoid inlining small_malloc_should_clear(szone, mspan, 0);

		if (NULL == p)
			return NULL;

		size_t offset = ((uintptr_t) p) & (alignment - 1); // p % alignment
		size_t pad = (0 == offset) ? 0 : alignment - offset; // p + pad achieves desired alignment

		msize_t msize = SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1);
		msize_t mpad = SMALL_MSIZE_FOR_BYTES(pad + SMALL_QUANTUM - 1);
		msize_t mwaste = mspan - msize - mpad; // excess blocks

		if (mpad > 0) {
			void *q = (void *)(((uintptr_t) p) + pad);

			// Mark q as block header and in-use, thus creating two blocks.
			magazine_t	*small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
																		  REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
																		  MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(p), SMALL_META_INDEX_FOR_PTR(p), mpad);
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), msize + mwaste);
			small_mag_ptr->mag_num_objects++;
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);

			// Give up mpad blocks beginning at p to the small free list
			// region_t r = SMALL_REGION_FOR_PTR(p);
			szone_free(szone, p); // avoid inlining free_small(szone, p, &r);

			p = q; // advance p to the desired alignment
		}
		if (mwaste > 0) {
			void *q = (void *)(((uintptr_t) p) + SMALL_BYTES_FOR_MSIZE(msize));
			// Mark q as block header and in-use, thus creating two blocks.
			magazine_t	*small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
																		  REGION_TRAILER_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)),
																		  MAGAZINE_INDEX_FOR_SMALL_REGION(SMALL_REGION_FOR_PTR(p)));
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(p), SMALL_META_INDEX_FOR_PTR(p), msize);
			small_meta_header_set_in_use(SMALL_META_HEADER_FOR_PTR(q), SMALL_META_INDEX_FOR_PTR(q), mwaste);
			small_mag_ptr->mag_num_objects++;
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);

			// Give up mwaste blocks beginning at q to the small free list
			// region_t r = SMALL_REGION_FOR_PTR(q);
			szone_free(szone, q); // avoid inlining free_small(szone, q, &r);
		}

		return p; // p has the desired size and alignment, and can later be free()'d

	} else if (szone->large_threshold < size && alignment <= vm_page_quanta_size) {
		return szone_malloc(szone, size); // Trivially satisfied by large

	} else {
		// ensure block allocated by large does not have a small-possible size
		size_t num_kernel_pages = round_page_quanta(MAX(szone->large_threshold + 1, size)) >> vm_page_quanta_shift;
		void *p;

		if (num_kernel_pages == 0)	/* Overflowed */
			p = NULL;
		else
			p = large_malloc(szone, num_kernel_pages, MAX(vm_page_quanta_shift, __builtin_ctz(alignment)), 0);

		return p;
	}
	/* NOTREACHED */
}

// given a size, returns the number of pointers allocated capable of holding
// that size, up to the limit specified by the 'count' argument.  These pointers
// are stored in the 'results' array, which must be allocated by the caller.
// may return zero, since this function is only a best attempt at allocating
// the pointers.  clients should be prepared to call malloc for any additional
// blocks they need.
static NOINLINE unsigned
szone_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count)
{
	msize_t	msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
	unsigned	found = 0;
	mag_index_t	mag_index = mag_get_thread_index(szone);
	magazine_t	*tiny_mag_ptr = &(szone->tiny_magazines[mag_index]);

	// only bother implementing this for tiny
	if (size > (NUM_TINY_SLOTS - 1)*TINY_QUANTUM)
		return 0;
	// make sure to return objects at least one quantum in size
	if (!msize)
		msize = 1;

	CHECK(szone, __PRETTY_FUNCTION__);

	// We must lock the zone now, since tiny_malloc_from_free_list assumes that
	// the caller has done so.
	SZONE_MAGAZINE_PTR_LOCK(szone, tiny_mag_ptr);

	// with the zone locked, allocate objects from the free list until all
	// sufficiently large objects have been exhausted, or we have met our quota
	// of objects to allocate.
	while (found < count) {
		void *ptr = tiny_malloc_from_free_list(szone, tiny_mag_ptr, mag_index, msize);
		if (!ptr)
			break;

		*results++ = ptr;
		found++;
	}
	SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
	return found;
}

/* Try caching the tiny_region and checking if the next ptr hits there. */
static NOINLINE void
szone_batch_free(szone_t *szone, void **to_be_freed, unsigned count)
{
	unsigned	cc = 0;
	void	*ptr;
	region_t	tiny_region = NULL;
	boolean_t	is_free;
	msize_t	msize;
	magazine_t	*tiny_mag_ptr = NULL;
	mag_index_t mag_index = -1;

	// frees all the pointers in to_be_freed
	// note that to_be_freed may be overwritten during the process
	if (!count)
		return;

	CHECK(szone, __PRETTY_FUNCTION__);
	while (cc < count) {
		ptr = to_be_freed[cc];
		if (ptr) {
			if (NULL == tiny_region || tiny_region != TINY_REGION_FOR_PTR(ptr)) { // region same as last iteration?
				if (tiny_mag_ptr) { // non-NULL iff magazine lock taken
					SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
					tiny_mag_ptr = NULL;
				}

				tiny_region = tiny_region_for_ptr_no_lock(szone, ptr);

				if (tiny_region) {
					tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																	REGION_TRAILER_FOR_TINY_REGION(tiny_region),
																	MAGAZINE_INDEX_FOR_TINY_REGION(tiny_region));
					mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(tiny_region);
				}
			}
			if (tiny_region) {
				// this is a tiny pointer
				if (TINY_INDEX_FOR_PTR(ptr) >= NUM_TINY_BLOCKS)
					break; // pointer to metadata; let the standard free deal with it
				msize = get_tiny_meta_header(ptr, &is_free);
				if (is_free)
					break; // a double free; let the standard free deal with it

				if (!tiny_free_no_lock(szone, tiny_mag_ptr, mag_index, tiny_region, ptr, msize)) {
					// Arrange to re-acquire magazine lock
					tiny_mag_ptr = NULL;
					tiny_region = NULL;
				}
				to_be_freed[cc] = NULL;
			} else {
				// No region in this zone claims ptr; let the standard free deal with it
				break;
			}
		}
		cc++;
	}

	if (tiny_mag_ptr) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
		tiny_mag_ptr = NULL;
	}

	CHECK(szone, __PRETTY_FUNCTION__);
	while (count--) {
		ptr = to_be_freed[count];
		if (ptr)
			szone_free(szone, ptr);
	}
}

// FIXME: Suppose one of the locks is held?
static void
szone_destroy(szone_t *szone)
{
	size_t		index;
	large_entry_t	*large;
	vm_range_t		range_to_deallocate;

#if LARGE_CACHE
	SZONE_LOCK(szone);

	/* disable any memory pressure responder */
	szone->flotsam_enabled = FALSE;

	// stack allocated copy of the death-row cache
	int idx = szone->large_entry_cache_oldest, idx_max = szone->large_entry_cache_newest;
	large_entry_t local_entry_cache[LARGE_ENTRY_CACHE_SIZE];

	memcpy((void *)local_entry_cache, (void *)szone->large_entry_cache, sizeof(local_entry_cache));

	szone->large_entry_cache_oldest = szone->large_entry_cache_newest = 0;
	szone->large_entry_cache[0].address = 0x0;
	szone->large_entry_cache[0].size = 0;
	szone->large_entry_cache_bytes = 0;
	szone->large_entry_cache_reserve_bytes = 0;

	SZONE_UNLOCK(szone);

	// deallocate the death-row cache outside the zone lock
	while (idx != idx_max) {
		deallocate_pages(szone, (void *) local_entry_cache[idx].address, local_entry_cache[idx].size, 0);
		if (++idx == LARGE_ENTRY_CACHE_SIZE) idx = 0;
	}
	if (0 != local_entry_cache[idx].address && 0 != local_entry_cache[idx].size) {
		deallocate_pages(szone, (void *) local_entry_cache[idx].address, local_entry_cache[idx].size, 0);
	}
#endif

	/* destroy large entries */
	index = szone->num_large_entries;
	while (index--) {
		large = szone->large_entries + index;
		if (large->address) {
			// we deallocate_pages, including guard pages
			deallocate_pages(szone, (void *)(large->address), large->size, szone->debug_flags);
		}
	}
	large_entries_free_no_lock(szone, szone->large_entries, szone->num_large_entries, &range_to_deallocate);
	if (range_to_deallocate.size)
		deallocate_pages(szone, (void *)range_to_deallocate.address, (size_t)range_to_deallocate.size, 0);

	/* destroy tiny regions */
	for (index = 0; index < szone->tiny_region_generation->num_regions_allocated; ++index)
		if ((HASHRING_OPEN_ENTRY != szone->tiny_region_generation->hashed_regions[index]) &&
			(HASHRING_REGION_DEALLOCATED != szone->tiny_region_generation->hashed_regions[index]))
			deallocate_pages(szone, szone->tiny_region_generation->hashed_regions[index], TINY_REGION_SIZE, 0);

	/* destroy small regions */
	for (index = 0; index < szone->small_region_generation->num_regions_allocated; ++index)
		if ((HASHRING_OPEN_ENTRY != szone->small_region_generation->hashed_regions[index]) &&
			(HASHRING_REGION_DEALLOCATED != szone->small_region_generation->hashed_regions[index]))
			deallocate_pages(szone, szone->small_region_generation->hashed_regions[index], SMALL_REGION_SIZE, 0);

	/* destroy region hash rings, if any */
	if (szone->tiny_region_generation->hashed_regions != szone->initial_tiny_regions) {
		size_t size = round_page_quanta(szone->tiny_region_generation->num_regions_allocated * sizeof(region_t));
		deallocate_pages(szone, szone->tiny_region_generation->hashed_regions, size, 0);
	}
	if (szone->small_region_generation->hashed_regions != szone->initial_small_regions) {
		size_t size = round_page_quanta(szone->small_region_generation->num_regions_allocated * sizeof(region_t));
		deallocate_pages(szone, szone->small_region_generation->hashed_regions, size, 0);
	}

	/* Now destroy the separate szone region */
	deallocate_pages(szone, (void *)&(szone->tiny_magazines[-1]), TINY_MAGAZINE_PAGED_SIZE, SCALABLE_MALLOC_ADD_GUARD_PAGES);
	deallocate_pages(szone, (void *)&(szone->small_magazines[-1]), SMALL_MAGAZINE_PAGED_SIZE, SCALABLE_MALLOC_ADD_GUARD_PAGES);
	deallocate_pages(szone, (void *)szone, SZONE_PAGED_SIZE, 0);
}

static NOINLINE size_t
szone_good_size(szone_t *szone, size_t size)
{
	msize_t msize;

	// Find a good size for this tiny allocation.
	if (size <= (NUM_TINY_SLOTS - 1) * TINY_QUANTUM) {
		msize = TINY_MSIZE_FOR_BYTES(size + TINY_QUANTUM - 1);
		if (!msize)
			msize = 1;
		return TINY_BYTES_FOR_MSIZE(msize);
	}

	// Find a good size for this small allocation.
	if (size <= szone->large_threshold) {
		msize = SMALL_MSIZE_FOR_BYTES(size + SMALL_QUANTUM - 1);
		if (!msize)
			msize = 1;
		return SMALL_BYTES_FOR_MSIZE(msize);
	}

	// Check for integer overflow on the size, since unlike the two cases above,
	// there is no upper bound on allocation size at this point.
	if (size > round_page_quanta(size))
		return (size_t)(-1LL);

#if DEBUG_MALLOC
	// It is not acceptable to see a size of zero here, since that means we
	// failed to catch a request for zero bytes in the tiny check, or the size
	// overflowed to zero during some arithmetic.
	if (size == 0)
		malloc_printf("szone_good_size() invariant broken %y\n", size);
#endif
	return round_page_quanta(size);
}

unsigned szone_check_counter = 0;
unsigned szone_check_start = 0;
unsigned szone_check_modulo = 1;

static NOINLINE boolean_t
szone_check_all(szone_t *szone, const char *function)
{
	size_t index;

	/* check tiny regions - chould check region count */
	for (index = 0; index < szone->tiny_region_generation->num_regions_allocated; ++index) {
		region_t tiny = szone->tiny_region_generation->hashed_regions[index];

		if (HASHRING_REGION_DEALLOCATED == tiny)
			continue;

		if (tiny) {
			magazine_t *tiny_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines,
																		REGION_TRAILER_FOR_TINY_REGION(tiny), MAGAZINE_INDEX_FOR_TINY_REGION(tiny));

			if (!tiny_check_region(szone, tiny)) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
				szone->debug_flags &= ~ CHECK_REGIONS;
				szone_error(szone, 1, "check: tiny region incorrect", NULL,
							"*** tiny region %ld incorrect szone_check_all(%s) counter=%d\n",
							index, function, szone_check_counter);
				return 0;
			}
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_mag_ptr);
		}
	}
	/* check tiny free lists */
	for (index = 0; index < NUM_TINY_SLOTS; ++index) {
		if (!tiny_free_list_check(szone, index)) {
			szone->debug_flags &= ~ CHECK_REGIONS;
			szone_error(szone, 1, "check: tiny free list incorrect", NULL,
						"*** tiny free list incorrect (slot=%ld) szone_check_all(%s) counter=%d\n",
						index, function, szone_check_counter);
			return 0;
		}
	}

	/* check small regions - could check region count */
	for (index = 0; index < szone->small_region_generation->num_regions_allocated; ++index) {
		region_t small = szone->small_region_generation->hashed_regions[index];

		if (HASHRING_REGION_DEALLOCATED == small)
			continue;

		if (small) {
			magazine_t *small_mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines,
																		 REGION_TRAILER_FOR_SMALL_REGION(small), MAGAZINE_INDEX_FOR_SMALL_REGION(small));

			if (!small_check_region(szone, small)) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
				szone->debug_flags &= ~ CHECK_REGIONS;
				szone_error(szone, 1, "check: small region incorrect", NULL,
							"*** small region %ld incorrect szone_check_all(%s) counter=%d\n",
							index, function, szone_check_counter);
				return 0;
			}
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_mag_ptr);
		}
	}
	/* check small free lists */
	for (index = 0; index < szone->num_small_slots; ++index) {
		if (!small_free_list_check(szone, index)) {
			szone->debug_flags &= ~ CHECK_REGIONS;
			szone_error(szone, 1, "check: small free list incorrect", NULL,
						"*** small free list incorrect (slot=%ld) szone_check_all(%s) counter=%d\n",
						index, function, szone_check_counter);
			return 0;
		}
	}

	return 1;
}

static boolean_t
szone_check(szone_t *szone)
{
	if ((++szone_check_counter % 10000) == 0)
		_malloc_printf(ASL_LEVEL_NOTICE, "at szone_check counter=%d\n", szone_check_counter);

	if (szone_check_counter < szone_check_start)
		return 1;

	if (szone_check_counter % szone_check_modulo)
		return 1;

	return szone_check_all(szone, "");
}

static kern_return_t
szone_ptr_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t zone_address,
							memory_reader_t reader, vm_range_recorder_t recorder)
{
	szone_t		*szone;
	kern_return_t	err;

	if (!reader) reader = _szone_default_reader;

	err = reader(task, zone_address, sizeof(szone_t), (void **)&szone);
	if (err) return err;

	err = tiny_in_use_enumerator(task, context, type_mask, szone, reader, recorder);
	if (err) return err;

	err = small_in_use_enumerator(task, context, type_mask, szone, reader, recorder);
	if (err) return err;

	err = large_in_use_enumerator(task, context, type_mask,
								  (vm_address_t)szone->large_entries, szone->num_large_entries, reader, recorder);
	return err;
}

// Following method is deprecated:  use scalable_zone_statistics instead
void
scalable_zone_info(malloc_zone_t *zone, unsigned *info_to_fill, unsigned count)
{
	szone_t	*szone = (void *)zone;
	unsigned	info[13];

	// We do not lock to facilitate debug

	size_t	s = 0;
	unsigned	t = 0;
	size_t	u = 0;
	mag_index_t mag_index;

	for (mag_index = -1; mag_index < szone->num_tiny_magazines; mag_index++) {
		s += szone->tiny_magazines[mag_index].mag_bytes_free_at_start;
		s += szone->tiny_magazines[mag_index].mag_bytes_free_at_end;
		t += szone->tiny_magazines[mag_index].mag_num_objects;
		u += szone->tiny_magazines[mag_index].mag_num_bytes_in_objects;
	}

	info[4] = t;
	info[5] = u;

	for (t = 0, u = 0, mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
		s += szone->small_magazines[mag_index].mag_bytes_free_at_start;
		s += szone->small_magazines[mag_index].mag_bytes_free_at_end;
		t += szone->small_magazines[mag_index].mag_num_objects;
		u += szone->small_magazines[mag_index].mag_num_bytes_in_objects;
	}

	info[6] = t;
	info[7] = u;

	info[8] = szone->num_large_objects_in_use;
	info[9] = szone->num_bytes_in_large_objects;

	info[10] = 0; // DEPRECATED szone->num_huge_entries;
	info[11] = 0; // DEPRECATED szone->num_bytes_in_huge_objects;

	info[12] = szone->debug_flags;

	info[0] = info[4] + info[6] + info[8] + info[10];
	info[1] = info[5] + info[7] + info[9] + info[11];

	info[3] = (szone->num_tiny_regions - szone->num_tiny_regions_dealloc) * TINY_REGION_SIZE +
	(szone->num_small_regions - szone->num_small_regions_dealloc) * SMALL_REGION_SIZE + info[9] + info[11];

	info[2] = info[3] - s;
	memcpy(info_to_fill, info, sizeof(unsigned)*count);
}

// FIXME: consistent picture requires locking!
static NOINLINE void
szone_print(szone_t *szone, boolean_t verbose)
{
	unsigned	info[13];
	size_t	index;
	region_t	region;

	scalable_zone_info((void *)szone, info, 13);
	_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
				   "Scalable zone %p: inUse=%u(%y) touched=%y allocated=%y flags=%d\n",
				   szone, info[0], info[1], info[2], info[3], info[12]);
	_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
				   "\ttiny=%u(%y) small=%u(%y) large=%u(%y) huge=%u(%y)\n",
				   info[4], info[5], info[6], info[7], info[8], info[9], info[10], info[11]);
	// tiny
	_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
				   "%lu tiny regions:\n", szone->num_tiny_regions);
	if (szone->num_tiny_regions_dealloc)
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
					   "[%lu tiny regions have been vm_deallocate'd]\n", szone->num_tiny_regions_dealloc);
	for (index = 0; index < szone->tiny_region_generation->num_regions_allocated; ++index) {
		region = szone->tiny_region_generation->hashed_regions[index];
		if (HASHRING_OPEN_ENTRY != region && HASHRING_REGION_DEALLOCATED != region) {
			mag_index_t mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(region);
			print_tiny_region(verbose, region,
							  (region == szone->tiny_magazines[mag_index].mag_last_region) ?
							  szone->tiny_magazines[mag_index].mag_bytes_free_at_start : 0,
							  (region == szone->tiny_magazines[mag_index].mag_last_region) ?
							  szone->tiny_magazines[mag_index].mag_bytes_free_at_end : 0);
		}
	}
	if (verbose)
		print_tiny_free_list(szone);
	// small
	_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
				   "%lu small regions:\n", szone->num_small_regions);
	if (szone->num_small_regions_dealloc)
		_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
					   "[%lu small regions have been vm_deallocate'd]\n", szone->num_small_regions_dealloc);
	for (index = 0; index < szone->small_region_generation->num_regions_allocated; ++index) {
		region = szone->small_region_generation->hashed_regions[index];
		if (HASHRING_OPEN_ENTRY != region && HASHRING_REGION_DEALLOCATED != region) {
			mag_index_t mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(region);
			print_small_region(szone, verbose, region,
							   (region == szone->small_magazines[mag_index].mag_last_region) ?
							   szone->small_magazines[mag_index].mag_bytes_free_at_start : 0,
							   (region == szone->small_magazines[mag_index].mag_last_region) ?
							   szone->small_magazines[mag_index].mag_bytes_free_at_end : 0);
		}
	}
	if (verbose)
		print_small_free_list(szone);
}

static void
szone_log(malloc_zone_t *zone, void *log_address)
{
	szone_t	*szone = (szone_t *)zone;

	szone->log_address = log_address;
}

// <rdar://problem/18001324>
// When forcing the lock on the entire zone, make sure we are out of the critical section in each magazine
static INLINE void
szone_force_lock_magazine(szone_t *szone, magazine_t *mag)
{
	while (1) {
		SZONE_MAGAZINE_PTR_LOCK(szone, mag);
		if (!mag->alloc_underway)
			return;

		SZONE_MAGAZINE_PTR_UNLOCK(szone, mag);
		yield();
	}
}

static void
szone_force_lock(szone_t *szone)
{
	mag_index_t i;

	for (i = 0; i < szone->num_tiny_magazines; ++i) {
		szone_force_lock_magazine(szone, &szone->tiny_magazines[i]);
	}
	szone_force_lock_magazine(szone, &szone->tiny_magazines[DEPOT_MAGAZINE_INDEX]);

	for (i = 0; i < szone->num_small_magazines; ++i) {
		szone_force_lock_magazine(szone, &szone->small_magazines[i]);
	}
	szone_force_lock_magazine(szone, &szone->small_magazines[DEPOT_MAGAZINE_INDEX]);

	SZONE_LOCK(szone);
}

static void
szone_force_unlock(szone_t *szone)
{
	mag_index_t i;

	SZONE_UNLOCK(szone);

	for (i = -1; i < szone->num_small_magazines; ++i) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone, (&(szone->small_magazines[i])));
	}

	for (i = -1; i < szone->num_tiny_magazines; ++i) {
		SZONE_MAGAZINE_PTR_UNLOCK(szone, (&(szone->tiny_magazines[i])));
	}
}

static boolean_t
szone_locked(szone_t *szone)
{
	mag_index_t i;
	int tookLock;

	tookLock = SZONE_TRY_LOCK(szone);
	if (tookLock == 0)
		return 1;
	SZONE_UNLOCK(szone);

	for (i = -1; i < szone->num_small_magazines; ++i) {
		tookLock = SZONE_MAGAZINE_PTR_TRY_LOCK(szone, (&(szone->small_magazines[i])));
		if (tookLock == 0)
			return 1;
		SZONE_MAGAZINE_PTR_UNLOCK(szone, (&(szone->small_magazines[i])));
	}

	for (i = -1; i < szone->num_tiny_magazines; ++i) {
		tookLock = SZONE_MAGAZINE_PTR_TRY_LOCK(szone, (&(szone->tiny_magazines[i])));
		if (tookLock == 0)
			return 1;
		SZONE_MAGAZINE_PTR_UNLOCK(szone, (&(szone->tiny_magazines[i])));
	}
	return 0;
}

static size_t
szone_pressure_relief(szone_t *szone, size_t goal)
{
	size_t total = 0;

#if MADVISE_PRESSURE_RELIEF
	mag_index_t mag_index;

	magazine_t *tiny_depot_ptr = (&szone->tiny_magazines[DEPOT_MAGAZINE_INDEX]);
	magazine_t *small_depot_ptr = (&szone->small_magazines[DEPOT_MAGAZINE_INDEX]);

	for (mag_index = 0; mag_index < szone->num_tiny_magazines; mag_index++) {
		size_t index;
		for (index = 0; index < szone->tiny_region_generation->num_regions_allocated; ++index) {
			SZONE_LOCK(szone);

			region_t tiny = szone->tiny_region_generation->hashed_regions[index];
			if (!tiny || tiny == HASHRING_REGION_DEALLOCATED) {
				SZONE_UNLOCK(szone);
				continue;
			}

			magazine_t *mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->tiny_magazines, REGION_TRAILER_FOR_TINY_REGION(tiny), MAGAZINE_INDEX_FOR_TINY_REGION(tiny));
			SZONE_UNLOCK(szone);

			/* Ordering is important here, the magazine of a region may potentially change
			 * during mag_lock_zine_for_region_trailer, so src_mag_index must be taken
			 * after we've obtained the lock.
			 */
			mag_index_t src_mag_index = MAGAZINE_INDEX_FOR_TINY_REGION(tiny);

			/* We can (and must) ignore magazines that are already in the recirc depot. */
			if (src_mag_index == DEPOT_MAGAZINE_INDEX) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, mag_ptr);
				continue;
			}

			if (tiny == mag_ptr->mag_last_region && (mag_ptr->mag_bytes_free_at_end || mag_ptr->mag_bytes_free_at_start)) {
				tiny_finalize_region(szone, mag_ptr);
			}

			/* Because this region is currently in use, we can't safely madvise it while
			 * it's attached to the magazine. For this operation we have to remove it from
			 * the current mag, attach it to the depot and then madvise.
			 */

			recirc_list_extract(szone, mag_ptr, REGION_TRAILER_FOR_TINY_REGION(tiny));
			int objects_in_use = tiny_free_detach_region(szone, mag_ptr, tiny);

			SZONE_MAGAZINE_PTR_LOCK(szone, tiny_depot_ptr);
			MAGAZINE_INDEX_FOR_TINY_REGION(tiny) = DEPOT_MAGAZINE_INDEX;
			REGION_TRAILER_FOR_TINY_REGION(tiny)->pinned_to_depot = 0;

			size_t bytes_inplay = tiny_free_reattach_region(szone, tiny_depot_ptr, tiny);

			/* Fix up the metadata of the target magazine while the region is in the depot. */
			mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
			mag_ptr->num_bytes_in_magazine -= TINY_REGION_PAYLOAD_BYTES;
			mag_ptr->mag_num_objects -= objects_in_use;

			/* Now we can drop the magazine lock of the source mag. */
			SZONE_MAGAZINE_PTR_UNLOCK(szone, mag_ptr);

			tiny_depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
			tiny_depot_ptr->num_bytes_in_magazine += TINY_REGION_PAYLOAD_BYTES;
			tiny_depot_ptr->mag_num_objects -= objects_in_use;

			recirc_list_splice_last(szone, tiny_depot_ptr, REGION_TRAILER_FOR_TINY_REGION(tiny));

			/* Actually do the scan, done holding the depot lock, the call will drop the lock
			 * around the actual madvise syscalls.
			 */
			tiny_free_scan_madvise_free(szone, tiny_depot_ptr, tiny);

			/* Now the region is in the recirc depot, the next allocations to require more
			 * blocks will come along and take one of these regions back out of the depot.
			 * As OS X madvise's reuse on an per-region basis, we leave as many of these
			 * regions in the depot as possible after memory pressure.
			 */
			SZONE_MAGAZINE_PTR_UNLOCK(szone, tiny_depot_ptr);
		}
	}

	for (mag_index = 0; mag_index < szone->num_small_magazines; mag_index++) {
		size_t index;
		for (index = 0; index < szone->small_region_generation->num_regions_allocated; ++index) {
			SZONE_LOCK(szone);

			region_t small = szone->small_region_generation->hashed_regions[index];
			if (!small || small == HASHRING_REGION_DEALLOCATED) {
				SZONE_UNLOCK(szone);
				continue;
			}

			magazine_t *mag_ptr = mag_lock_zine_for_region_trailer(szone, szone->small_magazines, REGION_TRAILER_FOR_SMALL_REGION(small), MAGAZINE_INDEX_FOR_SMALL_REGION(small));
			SZONE_UNLOCK(szone);

			/* Ordering is important here, the magazine of a region may potentially change
			 * during mag_lock_zine_for_region_trailer, so src_mag_index must be taken
			 * after we've obtained the lock.
			 */
			mag_index_t src_mag_index = MAGAZINE_INDEX_FOR_SMALL_REGION(small);

			/* We can (and must) ignore magazines that are already in the recirc depot. */
			if (src_mag_index == DEPOT_MAGAZINE_INDEX) {
				SZONE_MAGAZINE_PTR_UNLOCK(szone, mag_ptr);
				continue;
			}

			if (small == mag_ptr->mag_last_region && (mag_ptr->mag_bytes_free_at_end || mag_ptr->mag_bytes_free_at_start)) {
				small_finalize_region(szone, mag_ptr);
			}

			/* Because this region is currently in use, we can't safely madvise it while
			 * it's attached to the magazine. For this operation we have to remove it from
			 * the current mag, attach it to the depot and then madvise.
			 */

			recirc_list_extract(szone, mag_ptr, REGION_TRAILER_FOR_SMALL_REGION(small));
			int objects_in_use = small_free_detach_region(szone, mag_ptr, small);

			SZONE_MAGAZINE_PTR_LOCK(szone, small_depot_ptr);
			MAGAZINE_INDEX_FOR_SMALL_REGION(small) = DEPOT_MAGAZINE_INDEX;
			REGION_TRAILER_FOR_SMALL_REGION(small)->pinned_to_depot = 0;

			size_t bytes_inplay = small_free_reattach_region(szone, small_depot_ptr, small);

			/* Fix up the metadata of the target magazine while the region is in the depot. */
			mag_ptr->mag_num_bytes_in_objects -= bytes_inplay;
			mag_ptr->num_bytes_in_magazine -= SMALL_REGION_PAYLOAD_BYTES;
			mag_ptr->mag_num_objects -= objects_in_use;

			/* Now we can drop the magazine lock of the source mag. */
			SZONE_MAGAZINE_PTR_UNLOCK(szone, mag_ptr);

			small_depot_ptr->mag_num_bytes_in_objects += bytes_inplay;
			small_depot_ptr->num_bytes_in_magazine += SMALL_REGION_PAYLOAD_BYTES;
			small_depot_ptr->mag_num_objects -= objects_in_use;

			recirc_list_splice_last(szone, small_depot_ptr, REGION_TRAILER_FOR_SMALL_REGION(small));

			/* Actually do the scan, done holding the depot lock, the call will drop the lock
			 * around the actual madvise syscalls.
			 */
			small_free_scan_madvise_free(szone, small_depot_ptr, small);

			/* Now the region is in the recirc depot, the next allocations to require more
			 * blocks will come along and take one of these regions back out of the depot.
			 * As OS X madvise's reuse on an per-region basis, we leave as many of these
			 * regions in the depot as possible after memory pressure.
			 */
			SZONE_MAGAZINE_PTR_UNLOCK(szone, small_depot_ptr);
		}
	}
#endif

#if LARGE_CACHE
	if (szone->flotsam_enabled) {
		SZONE_LOCK(szone);

		// stack allocated copy of the death-row cache
		int idx = szone->large_entry_cache_oldest, idx_max = szone->large_entry_cache_newest;
		large_entry_t local_entry_cache[LARGE_ENTRY_CACHE_SIZE];

		memcpy((void *)local_entry_cache, (void *)szone->large_entry_cache, sizeof(local_entry_cache));

		szone->large_entry_cache_oldest = szone->large_entry_cache_newest = 0;
		szone->large_entry_cache[0].address = 0x0;
		szone->large_entry_cache[0].size = 0;
		szone->large_entry_cache_bytes = 0;
		szone->large_entry_cache_reserve_bytes = 0;

		szone->flotsam_enabled = FALSE;

		SZONE_UNLOCK(szone);

		// deallocate the death-row cache outside the zone lock
		size_t total = 0;
		while (idx != idx_max) {
			deallocate_pages(szone, (void *) local_entry_cache[idx].address, local_entry_cache[idx].size, 0);
			total += local_entry_cache[idx].size;
			if (++idx == LARGE_ENTRY_CACHE_SIZE) idx = 0;
		}
		if (0 != local_entry_cache[idx].address && 0 != local_entry_cache[idx].size) {
			deallocate_pages(szone, (void *) local_entry_cache[idx].address, local_entry_cache[idx].size, 0);
			total += local_entry_cache[idx].size;
		}
	}
#endif

	MAGMALLOC_PRESSURERELIEF((void *)szone, goal, total); // DTrace USDT Probe
	return total;
}

boolean_t
scalable_zone_statistics(malloc_zone_t *zone, malloc_statistics_t *stats, unsigned subzone)
{
	szone_t *szone = (szone_t *)zone;

	switch (subzone) {
		case 0:
		{
			size_t	s = 0;
			unsigned	t = 0;
			size_t	u = 0;
			mag_index_t mag_index;

			for (mag_index = -1; mag_index < szone->num_tiny_magazines; mag_index++) {
				s += szone->tiny_magazines[mag_index].mag_bytes_free_at_start;
				s += szone->tiny_magazines[mag_index].mag_bytes_free_at_end;
				t += szone->tiny_magazines[mag_index].mag_num_objects;
				u += szone->tiny_magazines[mag_index].mag_num_bytes_in_objects;
			}

			stats->blocks_in_use = t;
			stats->size_in_use = u;
			stats->size_allocated = (szone->num_tiny_regions - szone->num_tiny_regions_dealloc) * TINY_REGION_SIZE;
			stats->max_size_in_use = stats->size_allocated - s;
			return 1;
		}
		case 1:
		{
			size_t	s = 0;
			unsigned	t = 0;
			size_t	u = 0;
			mag_index_t mag_index;

			for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
				s += szone->small_magazines[mag_index].mag_bytes_free_at_start;
				s += szone->small_magazines[mag_index].mag_bytes_free_at_end;
				t += szone->small_magazines[mag_index].mag_num_objects;
				u += szone->small_magazines[mag_index].mag_num_bytes_in_objects;
			}

			stats->blocks_in_use = t;
			stats->size_in_use = u;
			stats->size_allocated = (szone->num_small_regions - szone->num_small_regions_dealloc) * SMALL_REGION_SIZE;
			stats->max_size_in_use = stats->size_allocated - s;
			return 1;
		}
		case 2:
			stats->blocks_in_use = szone->num_large_objects_in_use;
			stats->size_in_use = szone->num_bytes_in_large_objects;
			stats->max_size_in_use = stats->size_allocated = stats->size_in_use;
			return 1;
		case 3:
			stats->blocks_in_use = 0; // DEPRECATED szone->num_huge_entries;
			stats->size_in_use = 0; // DEPRECATED szone->num_bytes_in_huge_objects;
			stats->max_size_in_use = stats->size_allocated = 0;
			return 1;
	}
	return 0;
}

static void
szone_statistics(szone_t *szone, malloc_statistics_t *stats)
{
	size_t	large;

	size_t	s = 0;
	unsigned	t = 0;
	size_t	u = 0;
	mag_index_t mag_index;

	for (mag_index = -1; mag_index < szone->num_tiny_magazines; mag_index++) {
		s += szone->tiny_magazines[mag_index].mag_bytes_free_at_start;
		s += szone->tiny_magazines[mag_index].mag_bytes_free_at_end;
		t += szone->tiny_magazines[mag_index].mag_num_objects;
		u += szone->tiny_magazines[mag_index].mag_num_bytes_in_objects;
	}

	for (mag_index = -1; mag_index < szone->num_small_magazines; mag_index++) {
		s += szone->small_magazines[mag_index].mag_bytes_free_at_start;
		s += szone->small_magazines[mag_index].mag_bytes_free_at_end;
		t += szone->small_magazines[mag_index].mag_num_objects;
		u += szone->small_magazines[mag_index].mag_num_bytes_in_objects;
	}

	large = szone->num_bytes_in_large_objects + 0; // DEPRECATED szone->num_bytes_in_huge_objects;

	stats->blocks_in_use = t + szone->num_large_objects_in_use + 0; // DEPRECATED szone->num_huge_entries;
	stats->size_in_use = u + large;
	stats->max_size_in_use = stats->size_allocated =
	(szone->num_tiny_regions - szone->num_tiny_regions_dealloc) * TINY_REGION_SIZE +
	(szone->num_small_regions - szone->num_small_regions_dealloc) * SMALL_REGION_SIZE + large;
	// Now we account for the untouched areas
	stats->max_size_in_use -= s;
}

static void *
legacy_zeroing_large_malloc(szone_t *szone, size_t size) {
	if (size > LARGE_THRESHOLD) // Leopard and earlier returned a ZFOD range, so ...
		return szone_calloc(szone, 1, size); // Clear to zero always, ham-handedly touching in each page
	else
		return szone_malloc(szone, size);
}

static void *
legacy_zeroing_large_valloc(szone_t *szone, size_t size) {
	void *p = szone_valloc(szone, size);

	// Leopard and earlier returned a ZFOD range, so ...
	memset(p, 0, size); // Clear to zero always, ham-handedly touching in each page
	return p;
}

void zeroify_scalable_zone(malloc_zone_t *zone)
{
	szone_t	*szone = (szone_t *)zone;

	if (szone) {
		mprotect(szone, sizeof(szone->basic_zone), PROT_READ | PROT_WRITE);
		szone->basic_zone.malloc = (void *)legacy_zeroing_large_malloc;
		szone->basic_zone.valloc = (void *)legacy_zeroing_large_valloc;
		mprotect(szone, sizeof(szone->basic_zone), PROT_READ);
	}
}

static const struct malloc_introspection_t szone_introspect = {
	(void *)szone_ptr_in_use_enumerator,
	(void *)szone_good_size,
	(void *)szone_check,
	(void *)szone_print,
	szone_log,
	(void *)szone_force_lock,
	(void *)szone_force_unlock,
	(void *)szone_statistics,
	(void *)szone_locked,
	NULL, NULL, NULL, NULL, /* Zone enumeration version 7 and forward. */
}; // marked as const to spare the DATA section

malloc_zone_t *
create_scalable_zone(size_t initial_size, unsigned debug_flags)
{
	szone_t	*szone;
	uint64_t	hw_memsize = 0;

#if defined(__i386__) || defined(__x86_64__)
	if (_COMM_PAGE_VERSION_REQD > (*((uint16_t *)_COMM_PAGE_VERSION))) {
		malloc_printf("*** ERROR - comm page version mismatch.\n");
		exit(-1);
	}
#endif

	/* get memory for the zone. */
	szone = allocate_pages(NULL, SZONE_PAGED_SIZE, 0, 0, VM_MEMORY_MALLOC);
	if (!szone)
		return NULL;

	/* set up the szone structure */
#if 0
#warning CHECK_REGIONS enabled
	debug_flags |= CHECK_REGIONS;
#endif
#if 0
#warning LOG enabled
	szone->log_address = ~0;
#endif
	szone->trg[0].nextgen = &(szone->trg[1]);
	szone->trg[1].nextgen = &(szone->trg[0]);
	szone->tiny_region_generation = &(szone->trg[0]);

	szone->tiny_region_generation->hashed_regions = szone->initial_tiny_regions;
	szone->tiny_region_generation->num_regions_allocated = INITIAL_NUM_REGIONS;
	szone->tiny_region_generation->num_regions_allocated_shift = INITIAL_NUM_REGIONS_SHIFT;

	szone->srg[0].nextgen = &(szone->srg[1]);
	szone->srg[1].nextgen = &(szone->srg[0]);
	szone->small_region_generation = &(szone->srg[0]);

	szone->small_region_generation->hashed_regions = szone->initial_small_regions;
	szone->small_region_generation->num_regions_allocated = INITIAL_NUM_REGIONS;
	szone->small_region_generation->num_regions_allocated_shift = INITIAL_NUM_REGIONS_SHIFT;


	/*
	 * Initialize variables that size the free list for SMALL allocations based
	 * upon the amount of memory in the system.  Switch to a larger number of
	 * free list entries at 1GB.
	 */
#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__arm64__)
	if ((hw_memsize = *(uint64_t *)(uintptr_t)_COMM_PAGE_MEMORY_SIZE) >= (1ULL << 30))
#else
		size_t	uint64_t_size = sizeof(hw_memsize);

	if (0 == sysctlbyname("hw.memsize", &hw_memsize, &uint64_t_size, 0, 0) &&
		hw_memsize >= (1ULL << 30))
#endif
	{
		szone->is_largemem = 1;
		szone->num_small_slots = NUM_SMALL_SLOTS_LARGEMEM;
		szone->large_threshold = LARGE_THRESHOLD_LARGEMEM;
		szone->vm_copy_threshold = VM_COPY_THRESHOLD_LARGEMEM;
	} else {
		szone->is_largemem = 0;
		szone->num_small_slots = NUM_SMALL_SLOTS;
		szone->large_threshold = LARGE_THRESHOLD;
		szone->vm_copy_threshold = VM_COPY_THRESHOLD;
	}
#if LARGE_CACHE
	szone->large_entry_cache_reserve_limit =
	hw_memsize >> 10; // madvise(..., MADV_REUSABLE) death-row arrivals above this threshold [~0.1%]

	/* <rdar://problem/6610904> Reset protection when returning a previous large allocation? */
	int32_t libSystemVersion  = NSVersionOfLinkTimeLibrary("System");
	if ((-1 != libSystemVersion) && ((libSystemVersion >> 16) < 112) /* CFSystemVersionSnowLeopard */)
		szone->large_legacy_reset_mprotect = TRUE;
	else
		szone->large_legacy_reset_mprotect = FALSE;
#endif

	// Prepare ASLR
#if __i386__ || __x86_64__ || __arm64__ || TARGET_OS_EMBEDDED
#if __i386__
	uintptr_t stackbase = 0x8fe00000;
	int entropic_bits = 3;
#elif __x86_64__
	uintptr_t stackbase = USRSTACK64;
	int entropic_bits = 16;
#elif __arm64__
	uintptr_t stackbase = USRSTACK64;
	int entropic_bits = 7;
#else
	uintptr_t stackbase = USRSTACK;
	int entropic_bits = 3;
#endif

	// assert(((1 << entropic_bits) - 1) << SMALL_BLOCKS_ALIGN < (stackbase - MAXSSIZ - ENTROPIC_KABILLION));

	if (0 != _dyld_get_image_slide((const struct mach_header*)_NSGetMachExecuteHeader())) {
		if (0 == entropic_address) {
			uintptr_t t = stackbase - MAXSSIZ - ((uintptr_t) (malloc_entropy[1] & ((1 << entropic_bits) - 1)) << SMALL_BLOCKS_ALIGN);
			(void)__sync_bool_compare_and_swap(&entropic_limit, 0, t); // Just one initialization please
			(void)__sync_bool_compare_and_swap(&entropic_address, 0, t - ENTROPIC_KABILLION); // Just one initialization please
		}
		debug_flags &= ~DISABLE_ASLR;
	} else {
		// zero slide when ASLR has been disabled by boot-arg. Eliminate cloaking.
		malloc_entropy[0] = 0;
		malloc_entropy[1] = 0;
		debug_flags |= DISABLE_ASLR;
	}

#else
	malloc_entropy[0] = 0;
	malloc_entropy[1] = 0;
	debug_flags |= DISABLE_ASLR;
#endif

	// Initialize the security token.
	szone->cookie = (uintptr_t)malloc_entropy[0];

	szone->basic_zone.version = 8;
	szone->basic_zone.size = (void *)szone_size;
	szone->basic_zone.malloc = (void *)szone_malloc;
	szone->basic_zone.calloc = (void *)szone_calloc;
	szone->basic_zone.valloc = (void *)szone_valloc;
	szone->basic_zone.free = (void *)szone_free;
	szone->basic_zone.realloc = (void *)szone_realloc;
	szone->basic_zone.destroy = (void *)szone_destroy;
	szone->basic_zone.batch_malloc = (void *)szone_batch_malloc;
	szone->basic_zone.batch_free = (void *)szone_batch_free;
	szone->basic_zone.introspect = (struct malloc_introspection_t *)&szone_introspect;
	szone->basic_zone.memalign = (void *)szone_memalign;
	szone->basic_zone.free_definite_size = (void *)szone_free_definite_size;
	szone->basic_zone.pressure_relief = (void *)szone_pressure_relief;

	szone->basic_zone.reserved1 = 0; /* Set to zero once and for all as required by CFAllocator. */
	szone->basic_zone.reserved2 = 0; /* Set to zero once and for all as required by CFAllocator. */
	mprotect(szone, sizeof(szone->basic_zone), PROT_READ); /* Prevent overwriting the function pointers in basic_zone. */

	szone->debug_flags = debug_flags;
	_malloc_lock_init(&szone->large_szone_lock);

#if defined(__ppc__) || defined(__ppc64__)
	/*
	 * In the interest of compatibility for PPC applications executing via Rosetta,
	 * arrange to zero-fill allocations as occurred by side effect in Leopard and earlier.
	 */
	zeroify_scalable_zone((malloc_zone_t *)szone);
#endif

	szone->cpu_id_key = -1UL; // Unused.

	// Query the number of configured processors.
	// Uniprocessor case gets just one tiny and one small magazine (whose index is zero). This gives
	// the same behavior as the original scalable malloc. MP gets per-CPU magazines
	// that scale (way) better.
#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__arm64__)
	int nproc = *(uint8_t *)(uintptr_t)_COMM_PAGE_NCPUS;
#else
	int nproc = sysconf(_SC_NPROCESSORS_CONF);
#endif
	szone->num_tiny_magazines = (nproc > 1) ? MIN(nproc, TINY_MAX_MAGAZINES) : 1;

	// FIXME vm_allocate() based on number of configured CPUs
	magazine_t *tiny_magazines = allocate_pages(NULL, TINY_MAGAZINE_PAGED_SIZE, 0,
												SCALABLE_MALLOC_ADD_GUARD_PAGES, VM_MEMORY_MALLOC);
	if (NULL == tiny_magazines)
		return NULL;

	szone->tiny_magazines = &(tiny_magazines[1]); // szone->tiny_magazines[-1] is the Depot

	// The magazines are indexed in [0 .. (num_tiny_magazines - 1)]
	// Find the smallest power of 2 that exceeds (num_tiny_magazines - 1)
	szone->num_tiny_magazines_mask_shift = 0;
	int i = 1;
	while( i <= (szone->num_tiny_magazines - 1) ) {
		szone->num_tiny_magazines_mask_shift++;
		i <<= 1;
	}

	// Now if i <= TINY_MAX_MAGAZINES we'll never access tiny_magazines[] out of bounds.
	if (i > TINY_MAX_MAGAZINES) {
		malloc_printf("*** FATAL ERROR - magazine mask exceeds allocated magazines.\n");
		exit(-1);
	}

	// Reduce i by 1 to obtain a mask covering [0 .. (num_tiny_magazines - 1)]
	szone->num_tiny_magazines_mask = i - 1; // A mask used for hashing to a magazine index (and a safety aid)
	szone->last_tiny_advise = 0;

	// Init the tiny_magazine locks
	_malloc_lock_init(&szone->tiny_regions_lock);
	_malloc_lock_init(&szone->tiny_magazines[DEPOT_MAGAZINE_INDEX].magazine_lock);
	for (i = 0; i < szone->num_tiny_magazines; ++i) {
		_malloc_lock_init(&szone->tiny_magazines[i].magazine_lock);
	}

	szone->num_small_magazines = (nproc > 1) ? MIN(nproc, SMALL_MAX_MAGAZINES) : 1;

	// FIXME vm_allocate() based on number of configured CPUs
	magazine_t *small_magazines = allocate_pages(NULL, SMALL_MAGAZINE_PAGED_SIZE, 0,
												 SCALABLE_MALLOC_ADD_GUARD_PAGES, VM_MEMORY_MALLOC);
	if (NULL == small_magazines)
		return NULL;

	szone->small_magazines = &(small_magazines[1]); // szone->small_magazines[-1] is the Depot

	// The magazines are indexed in [0 .. (num_small_magazines - 1)]
	// Find the smallest power of 2 that exceeds (num_small_magazines - 1)
	szone->num_small_magazines_mask_shift = 0;
	while( i <= (szone->num_small_magazines - 1) ) {
		szone->num_small_magazines_mask_shift++;
		i <<= 1;
	}

	// Now if i <= SMALL_MAX_MAGAZINES we'll never access small_magazines[] out of bounds.
	if (i > SMALL_MAX_MAGAZINES) {
		malloc_printf("*** FATAL ERROR - magazine mask exceeds allocated magazines.\n");
		exit(-1);
	}

	// Reduce i by 1 to obtain a mask covering [0 .. (num_small_magazines - 1)]
	szone->num_small_magazines_mask = i - 1; // A mask used for hashing to a magazine index (and a safety aid)
	szone->last_small_advise = 0;

	// Init the small_magazine locks
	_malloc_lock_init(&szone->small_regions_lock);
	_malloc_lock_init(&szone->small_magazines[DEPOT_MAGAZINE_INDEX].magazine_lock);
	for (i = 0; i < szone->num_small_magazines; ++i) {
		_malloc_lock_init(&szone->small_magazines[i].magazine_lock);
	}

	CHECK(szone, __PRETTY_FUNCTION__);
	return (malloc_zone_t *)szone;
}

//
// purgeable zones have their own "large" allocation pool, but share "tiny" and "large"
// heaps with a helper_zone identified in the call to create_purgeable_zone()
//
static size_t
purgeable_size(szone_t *szone, const void *ptr)
{
	// Only claim our large allocations, leave the shared tiny/small for the helper zone to claim.
	return szone_size_try_large(szone, ptr);
}

static void *
purgeable_malloc(szone_t *szone, size_t size) {
	if (size <= szone->large_threshold)
		return szone_malloc(szone->helper_zone, size);
	else
		return szone_malloc(szone, size);
}

static void *
purgeable_calloc(szone_t *szone, size_t num_items, size_t size)
{
	size_t total_bytes = num_items * size;

	// Check for overflow of integer multiplication
	if (num_items > 1) {
#if __LP64__ /* size_t is uint64_t */
		if ((num_items | size) & 0xffffffff00000000ul) {
			// num_items or size equals or exceeds sqrt(2^64) == 2^32, appeal to wider arithmetic
			__uint128_t product = ((__uint128_t)num_items) * ((__uint128_t)size);
			if ((uint64_t)(product >> 64)) // compiles to test on upper register of register pair
				return NULL;
		}
#else /* size_t is uint32_t */
		if ((num_items | size) & 0xffff0000ul) {
			// num_items or size equals or exceeds sqrt(2^32) == 2^16, appeal to wider arithmetic
			uint64_t product = ((uint64_t)num_items) * ((uint64_t)size);
			if ((uint32_t)(product >> 32)) // compiles to test on upper register of register pair
				return NULL;
		}
#endif
	}

	if (total_bytes <= szone->large_threshold)
		return szone_calloc(szone->helper_zone, 1, total_bytes);
	else
		return szone_calloc(szone, 1, total_bytes);
}

static void *
purgeable_valloc(szone_t *szone, size_t size)
{
	if (size <= szone->large_threshold)
		return szone_valloc(szone->helper_zone, size);
	else
		return szone_valloc(szone, size);
}

static void
purgeable_free(szone_t *szone, void *ptr)
{
	large_entry_t	*entry;

	SZONE_LOCK(szone);
	entry = large_entry_for_pointer_no_lock(szone, ptr);
	SZONE_UNLOCK(szone);
	if (entry) {
		return free_large(szone, ptr);
	} else {
		return szone_free(szone->helper_zone, ptr);
	}
}

static void
purgeable_free_definite_size(szone_t *szone, void *ptr, size_t size)
{
	if (size <= szone->large_threshold)
		return szone_free_definite_size(szone->helper_zone, ptr, size);
	else
		return szone_free_definite_size(szone, ptr, size);
}

static void *
purgeable_realloc(szone_t *szone, void *ptr, size_t new_size)
{
	size_t old_size;

	if (NULL == ptr) {
		// If ptr is a null pointer, realloc() shall be equivalent to malloc() for the specified size.
		return purgeable_malloc(szone, new_size);
	} else if (0 == new_size) {
		// If size is 0 and ptr is not a null pointer, the object pointed to is freed.
		purgeable_free(szone, ptr);
		// If size is 0, either a null pointer or a unique pointer that can be successfully passed
		// to free() shall be returned.
		return purgeable_malloc(szone, 1);
	}

	old_size = purgeable_size(szone, ptr); // Now ptr can be safely size()'d
	if (!old_size)
		old_size = szone_size(szone->helper_zone, ptr);

	if (!old_size) {
		szone_error(szone, 1, "pointer being reallocated was not allocated", ptr, NULL);
		return NULL;
	}

	// Distinguish 4 cases: {oldsize, newsize} x { <= , > large_threshold }
	// and deal with the allocation crossing from the purgeable zone to the helper zone and vice versa.
	if (old_size <= szone->large_threshold) {
		if (new_size <= szone->large_threshold)
			return szone_realloc(szone->helper_zone, ptr, new_size);
		else {
			// allocation crosses from helper to purgeable zone
			void * new_ptr = purgeable_malloc(szone, new_size);
			if (new_ptr) {
				memcpy(new_ptr, ptr, old_size);
				szone_free_definite_size(szone->helper_zone, ptr, old_size);
			}
			return new_ptr; // in state VM_PURGABLE_NONVOLATILE
		}
	} else {
		if (new_size <= szone->large_threshold) {
			// allocation crosses from purgeable to helper zone
			void * new_ptr = szone_malloc(szone->helper_zone, new_size);
			if (new_ptr) {
				memcpy(new_ptr, ptr, new_size);
				purgeable_free_definite_size(szone, ptr, old_size);
			}
			return new_ptr;
		} else {
			void * new_ptr = purgeable_malloc(szone, new_size);
			if (new_ptr) {
				memcpy(new_ptr, ptr, MIN(old_size, new_size));
				purgeable_free_definite_size(szone, ptr, old_size);
			}
			return new_ptr; // in state VM_PURGABLE_NONVOLATILE
		}
	}
	/* NOTREACHED */
}

static void
purgeable_destroy(szone_t *szone)
{
	/* destroy large entries */
	size_t index = szone->num_large_entries;
	large_entry_t	*large;
	vm_range_t		range_to_deallocate;

	while (index--) {
		large = szone->large_entries + index;
		if (large->address) {
			// we deallocate_pages, including guard pages
			deallocate_pages(szone, (void *)(large->address), large->size, szone->debug_flags);
		}
	}
	large_entries_free_no_lock(szone, szone->large_entries, szone->num_large_entries, &range_to_deallocate);
	if (range_to_deallocate.size)
		deallocate_pages(szone, (void *)range_to_deallocate.address, (size_t)range_to_deallocate.size, 0);

	/* Now destroy the separate szone region */
	deallocate_pages(szone, (void *)szone, SZONE_PAGED_SIZE, 0);
}

static unsigned
purgeable_batch_malloc(szone_t *szone, size_t size, void **results, unsigned count)
{
	return szone_batch_malloc(szone->helper_zone, size, results, count);
}

static void
purgeable_batch_free(szone_t *szone, void **to_be_freed, unsigned count)
{
	return szone_batch_free(szone->helper_zone, to_be_freed, count);
}

static void *
purgeable_memalign(szone_t *szone, size_t alignment, size_t size)
{
	if (size <= szone->large_threshold)
		return szone_memalign(szone->helper_zone, alignment, size);
	else
		return szone_memalign(szone, alignment, size);
}

static kern_return_t
purgeable_ptr_in_use_enumerator(task_t task, void *context, unsigned type_mask, vm_address_t zone_address,
								memory_reader_t reader, vm_range_recorder_t recorder)
{
	szone_t		*szone;
	kern_return_t	err;

	if (!reader) reader = _szone_default_reader;

	err = reader(task, zone_address, sizeof(szone_t), (void **)&szone);
	if (err) return err;

	err = large_in_use_enumerator(task, context, type_mask,
								  (vm_address_t)szone->large_entries, szone->num_large_entries, reader, recorder);
	return err;
}

static size_t
purgeable_good_size(szone_t *szone, size_t size)
{
	if (size <= szone->large_threshold)
		return szone_good_size(szone->helper_zone, size);
	else
		return szone_good_size(szone, size);
}

static boolean_t
purgeable_check(szone_t *szone)
{
	return 1;
}

static void
purgeable_print(szone_t *szone, boolean_t verbose)
{
	_malloc_printf(MALLOC_PRINTF_NOLOG | MALLOC_PRINTF_NOPREFIX,
				   "Scalable zone %p: inUse=%u(%y) flags=%d\n",
				   szone, szone->num_large_objects_in_use, szone->num_bytes_in_large_objects, szone->debug_flags);
}

static void
purgeable_log(malloc_zone_t *zone, void *log_address)
{
	szone_t	*szone = (szone_t *)zone;

	szone->log_address = log_address;
}

static void
purgeable_force_lock(szone_t *szone)
{
	SZONE_LOCK(szone);
}

static void
purgeable_force_unlock(szone_t *szone)
{
	SZONE_UNLOCK(szone);
}

static void
purgeable_statistics(szone_t *szone, malloc_statistics_t *stats)
{
	stats->blocks_in_use = szone->num_large_objects_in_use;
	stats->size_in_use = stats->max_size_in_use = stats->size_allocated = szone->num_bytes_in_large_objects;
}

static boolean_t
purgeable_locked(szone_t *szone)
{
	int tookLock;

	tookLock = SZONE_TRY_LOCK(szone);
	if (tookLock == 0)
		return 1;
	SZONE_UNLOCK(szone);
	return 0;
}

static size_t
purgeable_pressure_relief(szone_t *szone, size_t goal)
{
	return szone_pressure_relief(szone, goal) + szone_pressure_relief(szone->helper_zone, goal);
}

static const struct malloc_introspection_t purgeable_introspect = {
	(void *)purgeable_ptr_in_use_enumerator,
	(void *)purgeable_good_size,
	(void *)purgeable_check,
	(void *)purgeable_print,
	purgeable_log,
	(void *)purgeable_force_lock,
	(void *)purgeable_force_unlock,
	(void *)purgeable_statistics,
	(void *)purgeable_locked,
	NULL, NULL, NULL, NULL, /* Zone enumeration version 7 and forward. */
}; // marked as const to spare the DATA section

__attribute__((visibility("hidden")))
malloc_zone_t *
create_purgeable_zone(size_t initial_size, malloc_zone_t *malloc_default_zone, unsigned debug_flags)
{
	szone_t	*szone;
	uint64_t	hw_memsize = 0;

	/* get memory for the zone. */
	szone = allocate_pages(NULL, SZONE_PAGED_SIZE, 0, 0, VM_MEMORY_MALLOC);
	if (!szone)
		return NULL;

	/* set up the szone structure */
#if 0
#warning LOG enabled
	szone->log_address = ~0;
#endif

#if defined(__i386__) || defined(__x86_64__) || defined(__arm__) || defined(__arm64__)
	hw_memsize = *(uint64_t *)(uintptr_t)_COMM_PAGE_MEMORY_SIZE;
#else
	size_t	uint64_t_size = sizeof(hw_memsize);

	sysctlbyname("hw.memsize", &hw_memsize, &uint64_t_size, 0, 0);
#endif

	szone->trg[0].nextgen = &(szone->trg[1]);
	szone->trg[1].nextgen = &(szone->trg[0]);
	szone->tiny_region_generation = &(szone->trg[0]);

	szone->tiny_region_generation->hashed_regions = szone->initial_tiny_regions;
	szone->tiny_region_generation->num_regions_allocated = INITIAL_NUM_REGIONS;
	szone->tiny_region_generation->num_regions_allocated_shift = INITIAL_NUM_REGIONS_SHIFT;

	szone->srg[0].nextgen = &(szone->srg[1]);
	szone->srg[1].nextgen = &(szone->srg[0]);
	szone->small_region_generation = &(szone->srg[0]);

	szone->small_region_generation->hashed_regions = szone->initial_small_regions;
	szone->small_region_generation->num_regions_allocated = INITIAL_NUM_REGIONS;
	szone->small_region_generation->num_regions_allocated_shift = INITIAL_NUM_REGIONS_SHIFT;

	/* Purgeable zone does not participate in the adaptive "largemem" sizing. */
	szone->is_largemem = 0;
	szone->large_threshold = LARGE_THRESHOLD;
	szone->vm_copy_threshold = VM_COPY_THRESHOLD;

#if LARGE_CACHE
	szone->large_entry_cache_reserve_limit =
	hw_memsize >> 10; // madvise(..., MADV_REUSABLE) death-row arrivals above this threshold [~0.1%]

	/* <rdar://problem/6610904> Reset protection when returning a previous large allocation? */
	int32_t libSystemVersion  = NSVersionOfLinkTimeLibrary("System");
	if ((-1 != libSystemVersion) && ((libSystemVersion >> 16) < 112) /* CFSystemVersionSnowLeopard */)
		szone->large_legacy_reset_mprotect = TRUE;
	else
		szone->large_legacy_reset_mprotect = FALSE;
#endif

	szone->basic_zone.version = 8;
	szone->basic_zone.size = (void *)purgeable_size;
	szone->basic_zone.malloc = (void *)purgeable_malloc;
	szone->basic_zone.calloc = (void *)purgeable_calloc;
	szone->basic_zone.valloc = (void *)purgeable_valloc;
	szone->basic_zone.free = (void *)purgeable_free;
	szone->basic_zone.realloc = (void *)purgeable_realloc;
	szone->basic_zone.destroy = (void *)purgeable_destroy;
	szone->basic_zone.batch_malloc = (void *)purgeable_batch_malloc;
	szone->basic_zone.batch_free = (void *)purgeable_batch_free;
	szone->basic_zone.introspect = (struct malloc_introspection_t *)&purgeable_introspect;
	szone->basic_zone.memalign = (void *)purgeable_memalign;
	szone->basic_zone.free_definite_size = (void *)purgeable_free_definite_size;
	szone->basic_zone.pressure_relief = (void *)purgeable_pressure_relief;

	szone->basic_zone.reserved1 = 0; /* Set to zero once and for all as required by CFAllocator. */
	szone->basic_zone.reserved2 = 0; /* Set to zero once and for all as required by CFAllocator. */
	mprotect(szone, sizeof(szone->basic_zone), PROT_READ); /* Prevent overwriting the function pointers in basic_zone. */

	szone->debug_flags = debug_flags | SCALABLE_MALLOC_PURGEABLE;

	/* Purgeable zone does not support SCALABLE_MALLOC_ADD_GUARD_PAGES. */
	if (szone->debug_flags & SCALABLE_MALLOC_ADD_GUARD_PAGES) {
		_malloc_printf(ASL_LEVEL_INFO, "purgeable zone does not support guard pages\n");
		szone->debug_flags &= ~SCALABLE_MALLOC_ADD_GUARD_PAGES;
	}

	_malloc_lock_init(&szone->large_szone_lock);

	szone->helper_zone = (struct szone_s *)malloc_default_zone;

	CHECK(szone, __PRETTY_FUNCTION__);
	return (malloc_zone_t *)szone;
}

/*
 * For use by CheckFix: create a new zone whose behavior is, apart from
 * the use of death-row and per-CPU magazines, that of Leopard.
 */
static NOINLINE void *
legacy_valloc(szone_t *szone, size_t size)
{
	void	*ptr;
	size_t num_kernel_pages;

	num_kernel_pages = round_page_quanta(size) >> vm_page_quanta_shift;
	ptr = large_malloc(szone, num_kernel_pages, 0, TRUE);
#if DEBUG_MALLOC
	if (LOG(szone, ptr))
		malloc_printf("legacy_valloc returned %p\n", ptr);
#endif
	return ptr;
}

__attribute__((visibility("hidden")))
malloc_zone_t *
create_legacy_scalable_zone(size_t initial_size, unsigned debug_flags)
{
	malloc_zone_t *mzone = create_scalable_zone(initial_size, debug_flags);
	szone_t	*szone = (szone_t *)mzone;

	if (!szone)
		return NULL;

	szone->is_largemem = 0;
	szone->num_small_slots = NUM_SMALL_SLOTS;
	szone->large_threshold = LARGE_THRESHOLD;
	szone->vm_copy_threshold = VM_COPY_THRESHOLD;

	mprotect(szone, sizeof(szone->basic_zone), PROT_READ | PROT_WRITE);
	szone->basic_zone.valloc = (void *)legacy_valloc;
	szone->basic_zone.free_definite_size = NULL;
	mprotect(szone, sizeof(szone->basic_zone), PROT_READ);

	return mzone;
}

/********* Support code for emacs unexec ************/

/* History of freezedry version numbers:
 *
 * 1) Old malloc (before the scalable malloc implementation in this file
 *    existed).
 * 2) Original freezedrying code for scalable malloc.  This code was apparently
 *    based on the old freezedrying code and was fundamentally flawed in its
 *    assumption that tracking allocated memory regions was adequate to fake
 *    operations on freezedried memory.  This doesn't work, since scalable
 *    malloc does not store flags in front of large page-aligned allocations.
 * 3) Original szone-based freezedrying code.
 * 4) Fresher malloc with tiny zone
 * 5) 32/64bit compatible malloc
 * 6) Metadata within 1MB and 8MB region for tiny and small
 *
 * No version backward compatibility is provided, but the version number does
 * make it possible for malloc_jumpstart() to return an error if the application
 * was freezedried with an older version of malloc.
 */
#define MALLOC_FREEZEDRY_VERSION 6

typedef struct {
	unsigned	version;
	unsigned	nszones;
	szone_t	*szones;
} malloc_frozen;

static void *
frozen_malloc(szone_t *zone, size_t new_size)
{
	return malloc(new_size);
}

static void *
frozen_calloc(szone_t *zone, size_t num_items, size_t size)
{
	return calloc(num_items, size);
}

static void *
frozen_valloc(szone_t *zone, size_t new_size)
{
	return valloc(new_size);
}

static void *
frozen_realloc(szone_t *zone, void *ptr, size_t new_size)
{
	size_t	old_size = szone_size(zone, ptr);
	void	*new_ptr;

	if (new_size <= old_size) {
		return ptr;
	}
	new_ptr = malloc(new_size);
	if (old_size > 0) {
		memcpy(new_ptr, ptr, old_size);
	}
	return new_ptr;
}

static void
frozen_free(szone_t *zone, void *ptr)
{
}

static void
frozen_destroy(szone_t *zone)
{
}

/********* Pseudo-private API for emacs unexec ************/

/*
 * malloc_freezedry() records all of the szones in use, so that they can be
 * partially reconstituted by malloc_jumpstart().  Due to the differences
 * between reconstituted memory regions and those created by the szone code,
 * care is taken not to reallocate from the freezedried memory, except in the
 * case of a non-growing realloc().
 *
 * Due to the flexibility provided by the zone registration mechanism, it is
 * impossible to implement generic freezedrying for any zone type.  This code
 * only handles applications that use the szone allocator, so malloc_freezedry()
 * returns 0 (error) if any non-szone zones are encountered.
 */

uintptr_t
malloc_freezedry(void)
{
	extern unsigned malloc_num_zones;
	extern malloc_zone_t **malloc_zones;
	malloc_frozen *data;
	unsigned i;

	/* Allocate space in which to store the freezedry state. */
	data = (malloc_frozen *) malloc(sizeof(malloc_frozen));

	/* Set freezedry version number so that malloc_jumpstart() can check for compatibility. */
	data->version = MALLOC_FREEZEDRY_VERSION;

	/* Allocate the array of szone pointers. */
	data->nszones = malloc_num_zones;
	data->szones = (szone_t *) calloc(malloc_num_zones, sizeof(szone_t));

	/*
	 * Fill in the array of szone structures.  They are copied rather than
	 * referenced, since the originals are likely to be clobbered during malloc
	 * initialization.
	 */
	for (i = 0; i < malloc_num_zones; i++) {
		if (strcmp(malloc_zones[i]->zone_name, "DefaultMallocZone")) {
			/* Unknown zone type. */
			free(data->szones);
			free(data);
			return 0;
		}
		memcpy(&data->szones[i], malloc_zones[i], sizeof(szone_t));
	}

	return((uintptr_t)data);
}

int
malloc_jumpstart(uintptr_t cookie)
{
	malloc_frozen *data = (malloc_frozen *)cookie;
	unsigned i;

	if (data->version != MALLOC_FREEZEDRY_VERSION) {
		/* Unsupported freezedry version. */
		return 1;
	}

	for (i = 0; i < data->nszones; i++) {
		/* Set function pointers.  Even the functions that stay the same must be
		 * set, since there are no guarantees that they will be mapped to the
		 * same addresses. */
		data->szones[i].basic_zone.size = (void *) szone_size;
		data->szones[i].basic_zone.malloc = (void *) frozen_malloc;
		data->szones[i].basic_zone.calloc = (void *) frozen_calloc;
		data->szones[i].basic_zone.valloc = (void *) frozen_valloc;
		data->szones[i].basic_zone.free = (void *) frozen_free;
		data->szones[i].basic_zone.realloc = (void *) frozen_realloc;
		data->szones[i].basic_zone.destroy = (void *) frozen_destroy;
		data->szones[i].basic_zone.introspect = (struct malloc_introspection_t *)&szone_introspect;

		/* Register the freezedried zone. */
		malloc_zone_register(&data->szones[i].basic_zone);
	}

	return 0;
}

/* vim: set noet:ts=4:sw=4:cindent: */