1/*
2 *  Copyright (C) 2007-2010 Lawrence Livermore National Security, LLC.
3 *  Copyright (C) 2007 The Regents of the University of California.
4 *  Produced at Lawrence Livermore National Laboratory (cf, DISCLAIMER).
5 *  Written by Brian Behlendorf <behlendorf1@llnl.gov>.
6 *  UCRL-CODE-235197
7 *
8 *  This file is part of the SPL, Solaris Porting Layer.
9 *
10 *  The SPL is free software; you can redistribute it and/or modify it
11 *  under the terms of the GNU General Public License as published by the
12 *  Free Software Foundation; either version 2 of the License, or (at your
13 *  option) any later version.
14 *
15 *  The SPL is distributed in the hope that it will be useful, but WITHOUT
16 *  ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
17 *  FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
18 *  for more details.
19 *
20 *  You should have received a copy of the GNU General Public License along
21 *  with the SPL.  If not, see <http://www.gnu.org/licenses/>.
22 */
23
24#ifndef _SPL_VMEM_H
25#define	_SPL_VMEM_H
26
27#include <sys/kmem.h>
28#include <linux/sched.h>
29#include <linux/vmalloc.h>
30
31typedef struct vmem { } vmem_t;
32
33/*
34 * Memory allocation interfaces
35 */
36#define	VMEM_ALLOC	0x01
37#define	VMEM_FREE	0x02
38
39#ifndef VMALLOC_TOTAL
40#define	VMALLOC_TOTAL	(VMALLOC_END - VMALLOC_START)
41#endif
42
43/*
44 * vmem_* is an interface to a low level arena-based memory allocator on
45 * Illumos that is used to allocate virtual address space. The kmem SLAB
46 * allocator allocates slabs from it. Then the generic allocation functions
47 * kmem_{alloc,zalloc,free}() are layered on top of SLAB allocators.
48 *
49 * On Linux, the primary means of doing allocations is via kmalloc(), which
50 * is similarly layered on top of something called the buddy allocator. The
51 * buddy allocator is not available to kernel modules, it uses physical
52 * memory addresses rather than virtual memory addresses and is prone to
53 * fragmentation.
54 *
55 * Linux sets aside a relatively small address space for in-kernel virtual
56 * memory from which allocations can be done using vmalloc().  It might seem
57 * like a good idea to use vmalloc() to implement something similar to
58 * Illumos' allocator. However, this has the following problems:
59 *
60 * 1. Page directory table allocations are hard coded to use GFP_KERNEL.
61 *    Consequently, any KM_PUSHPAGE or KM_NOSLEEP allocations done using
62 *    vmalloc() will not have proper semantics.
63 *
64 * 2. Address space exhaustion is a real issue on 32-bit platforms where
65 *    only a few 100MB are available. The kernel will handle it by spinning
66 *    when it runs out of address space.
67 *
68 * 3. All vmalloc() allocations and frees are protected by a single global
69 *    lock which serializes all allocations.
70 *
71 * 4. Accessing /proc/meminfo and /proc/vmallocinfo will iterate the entire
72 *    list. The former will sum the allocations while the latter will print
73 *    them to user space in a way that user space can keep the lock held
74 *    indefinitely.  When the total number of mapped allocations is large
75 *    (several 100,000) a large amount of time will be spent waiting on locks.
76 *
77 * 5. Linux has a wait_on_bit() locking primitive that assumes physical
78 *    memory is used, it simply does not work on virtual memory.  Certain
79 *    Linux structures (e.g. the superblock) use them and might be embedded
80 *    into a structure from Illumos.  This makes using Linux virtual memory
81 *    unsafe in certain situations.
82 *
83 * It follows that we cannot obtain identical semantics to those on Illumos.
84 * Consequently, we implement the kmem_{alloc,zalloc,free}() functions in
85 * such a way that they can be used as drop-in replacements for small vmem_*
86 * allocations (8MB in size or smaller) and map vmem_{alloc,zalloc,free}()
87 * to them.
88 */
89
90#define	vmem_alloc(sz, fl)	spl_vmem_alloc((sz), (fl), __func__, __LINE__)
91#define	vmem_zalloc(sz, fl)	spl_vmem_zalloc((sz), (fl), __func__, __LINE__)
92#define	vmem_free(ptr, sz)	spl_vmem_free((ptr), (sz))
93
94extern void *spl_vmem_alloc(size_t sz, int fl, const char *func, int line)
95    __attribute__((malloc, alloc_size(1)));
96extern void *spl_vmem_zalloc(size_t sz, int fl, const char *func, int line)
97    __attribute__((malloc, alloc_size(1)));
98extern void spl_vmem_free(const void *ptr, size_t sz);
99
100int spl_vmem_init(void);
101void spl_vmem_fini(void);
102
103#endif	/* _SPL_VMEM_H */
104