malloc.c revision 38816
1/*- 2 * Copyright (c) 1983 Regents of the University of California. 3 * All rights reserved. 4 * 5 * Redistribution and use in source and binary forms, with or without 6 * modification, are permitted provided that the following conditions 7 * are met: 8 * 1. Redistributions of source code must retain the above copyright 9 * notice, this list of conditions and the following disclaimer. 10 * 2. Redistributions in binary form must reproduce the above copyright 11 * notice, this list of conditions and the following disclaimer in the 12 * documentation and/or other materials provided with the distribution. 13 * 3. All advertising materials mentioning features or use of this software 14 * must display the following acknowledgement: 15 * This product includes software developed by the University of 16 * California, Berkeley and its contributors. 17 * 4. Neither the name of the University nor the names of its contributors 18 * may be used to endorse or promote products derived from this software 19 * without specific prior written permission. 20 * 21 * THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND 22 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 23 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 24 * ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE 25 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 26 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 27 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 28 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 29 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 30 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 31 * SUCH DAMAGE. 32 */ 33 34#if defined(LIBC_SCCS) && !defined(lint) 35/*static char *sccsid = "from: @(#)malloc.c 5.11 (Berkeley) 2/23/91";*/ 36static char *rcsid = "$Id: malloc.c,v 1.1.1.1 1998/03/07 19:24:35 jdp Exp $"; 37#endif /* LIBC_SCCS and not lint */ 38 39/* 40 * malloc.c (Caltech) 2/21/82 41 * Chris Kingsley, kingsley@cit-20. 42 * 43 * This is a very fast storage allocator. It allocates blocks of a small 44 * number of different sizes, and keeps free lists of each size. Blocks that 45 * don't exactly fit are passed up to the next larger size. In this 46 * implementation, the available sizes are 2^n-4 (or 2^n-10) bytes long. 47 * This is designed for use in a virtual memory environment. 48 */ 49 50#include <sys/types.h> 51#include <err.h> 52#include <stdlib.h> 53#include <string.h> 54#include <unistd.h> 55#include <sys/param.h> 56#include <sys/mman.h> 57#ifndef BSD 58#define MAP_COPY MAP_PRIVATE 59#define MAP_FILE 0 60#define MAP_ANON 0 61#endif 62 63#ifndef BSD /* Need do better than this */ 64#define NEED_DEV_ZERO 1 65#endif 66 67#define NULL 0 68 69static void morecore(); 70static int findbucket(); 71 72/* 73 * Pre-allocate mmap'ed pages 74 */ 75#define NPOOLPAGES (32*1024/pagesz) 76static caddr_t pagepool_start, pagepool_end; 77static int morepages(); 78 79/* 80 * The overhead on a block is at least 4 bytes. When free, this space 81 * contains a pointer to the next free block, and the bottom two bits must 82 * be zero. When in use, the first byte is set to MAGIC, and the second 83 * byte is the size index. The remaining bytes are for alignment. 84 * If range checking is enabled then a second word holds the size of the 85 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC). 86 * The order of elements is critical: ov_magic must overlay the low order 87 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern. 88 */ 89union overhead { 90 union overhead *ov_next; /* when free */ 91 struct { 92 u_char ovu_magic; /* magic number */ 93 u_char ovu_index; /* bucket # */ 94#ifdef RCHECK 95 u_short ovu_rmagic; /* range magic number */ 96 u_int ovu_size; /* actual block size */ 97#endif 98 } ovu; 99#define ov_magic ovu.ovu_magic 100#define ov_index ovu.ovu_index 101#define ov_rmagic ovu.ovu_rmagic 102#define ov_size ovu.ovu_size 103}; 104 105#define MAGIC 0xef /* magic # on accounting info */ 106#define RMAGIC 0x5555 /* magic # on range info */ 107 108#ifdef RCHECK 109#define RSLOP sizeof (u_short) 110#else 111#define RSLOP 0 112#endif 113 114/* 115 * nextf[i] is the pointer to the next free block of size 2^(i+3). The 116 * smallest allocatable block is 8 bytes. The overhead information 117 * precedes the data area returned to the user. 118 */ 119#define NBUCKETS 30 120static union overhead *nextf[NBUCKETS]; 121extern char *sbrk(); 122 123static int pagesz; /* page size */ 124static int pagebucket; /* page size bucket */ 125 126#ifdef MSTATS 127/* 128 * nmalloc[i] is the difference between the number of mallocs and frees 129 * for a given block size. 130 */ 131static u_int nmalloc[NBUCKETS]; 132#include <stdio.h> 133#endif 134 135#if defined(MALLOC_DEBUG) || defined(RCHECK) 136#define ASSERT(p) if (!(p)) botch("p") 137#include <stdio.h> 138static void 139botch(s) 140 char *s; 141{ 142 fprintf(stderr, "\r\nassertion botched: %s\r\n", s); 143 (void) fflush(stderr); /* just in case user buffered it */ 144 abort(); 145} 146#else 147#define ASSERT(p) 148#endif 149 150/* Debugging stuff */ 151extern void xprintf(const char *, ...); 152#define TRACE() xprintf("TRACE %s:%d\n", __FILE__, __LINE__) 153 154void * 155malloc(nbytes) 156 size_t nbytes; 157{ 158 register union overhead *op; 159 register int bucket; 160 register long n; 161 register unsigned amt; 162 163 /* 164 * First time malloc is called, setup page size and 165 * align break pointer so all data will be page aligned. 166 */ 167 if (pagesz == 0) { 168 pagesz = n = getpagesize(); 169 if (morepages(NPOOLPAGES) == 0) 170 return NULL; 171 op = (union overhead *)(pagepool_start); 172 n = n - sizeof (*op) - ((long)op & (n - 1)); 173 if (n < 0) 174 n += pagesz; 175 if (n) { 176 pagepool_start += n; 177 } 178 bucket = 0; 179 amt = 8; 180 while (pagesz > amt) { 181 amt <<= 1; 182 bucket++; 183 } 184 pagebucket = bucket; 185 } 186 /* 187 * Convert amount of memory requested into closest block size 188 * stored in hash buckets which satisfies request. 189 * Account for space used per block for accounting. 190 */ 191 if (nbytes <= (n = pagesz - sizeof (*op) - RSLOP)) { 192#ifndef RCHECK 193 amt = 8; /* size of first bucket */ 194 bucket = 0; 195#else 196 amt = 16; /* size of first bucket */ 197 bucket = 1; 198#endif 199 n = -(sizeof (*op) + RSLOP); 200 } else { 201 amt = pagesz; 202 bucket = pagebucket; 203 } 204 while (nbytes > amt + n) { 205 amt <<= 1; 206 if (amt == 0) 207 return (NULL); 208 bucket++; 209 } 210 /* 211 * If nothing in hash bucket right now, 212 * request more memory from the system. 213 */ 214 if ((op = nextf[bucket]) == NULL) { 215 morecore(bucket); 216 if ((op = nextf[bucket]) == NULL) 217 return (NULL); 218 } 219 /* remove from linked list */ 220 nextf[bucket] = op->ov_next; 221 op->ov_magic = MAGIC; 222 op->ov_index = bucket; 223#ifdef MSTATS 224 nmalloc[bucket]++; 225#endif 226#ifdef RCHECK 227 /* 228 * Record allocated size of block and 229 * bound space with magic numbers. 230 */ 231 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 232 op->ov_rmagic = RMAGIC; 233 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 234#endif 235 return ((char *)(op + 1)); 236} 237 238/* 239 * Allocate more memory to the indicated bucket. 240 */ 241static void 242morecore(bucket) 243 int bucket; 244{ 245 register union overhead *op; 246 register int sz; /* size of desired block */ 247 int amt; /* amount to allocate */ 248 int nblks; /* how many blocks we get */ 249 250 /* 251 * sbrk_size <= 0 only for big, FLUFFY, requests (about 252 * 2^30 bytes on a VAX, I think) or for a negative arg. 253 */ 254 sz = 1 << (bucket + 3); 255#ifdef MALLOC_DEBUG 256 ASSERT(sz > 0); 257#else 258 if (sz <= 0) 259 return; 260#endif 261 if (sz < pagesz) { 262 amt = pagesz; 263 nblks = amt / sz; 264 } else { 265 amt = sz + pagesz; 266 nblks = 1; 267 } 268 if (amt > pagepool_end - pagepool_start) 269 if (morepages(amt/pagesz + NPOOLPAGES) == 0) 270 return; 271 op = (union overhead *)pagepool_start; 272 pagepool_start += amt; 273 274 /* 275 * Add new memory allocated to that on 276 * free list for this hash bucket. 277 */ 278 nextf[bucket] = op; 279 while (--nblks > 0) { 280 op->ov_next = (union overhead *)((caddr_t)op + sz); 281 op = (union overhead *)((caddr_t)op + sz); 282 } 283} 284 285void 286free(cp) 287 void *cp; 288{ 289 register int size; 290 register union overhead *op; 291 292 if (cp == NULL) 293 return; 294 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 295#ifdef MALLOC_DEBUG 296 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 297#else 298 if (op->ov_magic != MAGIC) 299 return; /* sanity */ 300#endif 301#ifdef RCHECK 302 ASSERT(op->ov_rmagic == RMAGIC); 303 ASSERT(*(u_short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC); 304#endif 305 size = op->ov_index; 306 ASSERT(size < NBUCKETS); 307 op->ov_next = nextf[size]; /* also clobbers ov_magic */ 308 nextf[size] = op; 309#ifdef MSTATS 310 nmalloc[size]--; 311#endif 312} 313 314/* 315 * When a program attempts "storage compaction" as mentioned in the 316 * old malloc man page, it realloc's an already freed block. Usually 317 * this is the last block it freed; occasionally it might be farther 318 * back. We have to search all the free lists for the block in order 319 * to determine its bucket: 1st we make one pass thru the lists 320 * checking only the first block in each; if that fails we search 321 * ``realloc_srchlen'' blocks in each list for a match (the variable 322 * is extern so the caller can modify it). If that fails we just copy 323 * however many bytes was given to realloc() and hope it's not huge. 324 */ 325int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ 326 327void * 328realloc(cp, nbytes) 329 void *cp; 330 size_t nbytes; 331{ 332 register u_int onb; 333 register int i; 334 union overhead *op; 335 char *res; 336 int was_alloced = 0; 337 338 if (cp == NULL) 339 return (malloc(nbytes)); 340 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 341 if (op->ov_magic == MAGIC) { 342 was_alloced++; 343 i = op->ov_index; 344 } else { 345 /* 346 * Already free, doing "compaction". 347 * 348 * Search for the old block of memory on the 349 * free list. First, check the most common 350 * case (last element free'd), then (this failing) 351 * the last ``realloc_srchlen'' items free'd. 352 * If all lookups fail, then assume the size of 353 * the memory block being realloc'd is the 354 * largest possible (so that all "nbytes" of new 355 * memory are copied into). Note that this could cause 356 * a memory fault if the old area was tiny, and the moon 357 * is gibbous. However, that is very unlikely. 358 */ 359 if ((i = findbucket(op, 1)) < 0 && 360 (i = findbucket(op, realloc_srchlen)) < 0) 361 i = NBUCKETS; 362 } 363 onb = 1 << (i + 3); 364 if (onb < pagesz) 365 onb -= sizeof (*op) + RSLOP; 366 else 367 onb += pagesz - sizeof (*op) - RSLOP; 368 /* avoid the copy if same size block */ 369 if (was_alloced) { 370 if (i) { 371 i = 1 << (i + 2); 372 if (i < pagesz) 373 i -= sizeof (*op) + RSLOP; 374 else 375 i += pagesz - sizeof (*op) - RSLOP; 376 } 377 if (nbytes <= onb && nbytes > i) { 378#ifdef RCHECK 379 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 380 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 381#endif 382 return(cp); 383 } else 384 free(cp); 385 } 386 if ((res = malloc(nbytes)) == NULL) 387 return (NULL); 388 if (cp != res) /* common optimization if "compacting" */ 389 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 390 return (res); 391} 392 393/* 394 * Search ``srchlen'' elements of each free list for a block whose 395 * header starts at ``freep''. If srchlen is -1 search the whole list. 396 * Return bucket number, or -1 if not found. 397 */ 398static int 399findbucket(freep, srchlen) 400 union overhead *freep; 401 int srchlen; 402{ 403 register union overhead *p; 404 register int i, j; 405 406 for (i = 0; i < NBUCKETS; i++) { 407 j = 0; 408 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { 409 if (p == freep) 410 return (i); 411 j++; 412 } 413 } 414 return (-1); 415} 416 417#ifdef MSTATS 418/* 419 * mstats - print out statistics about malloc 420 * 421 * Prints two lines of numbers, one showing the length of the free list 422 * for each size category, the second showing the number of mallocs - 423 * frees for each size category. 424 */ 425mstats(s) 426 char *s; 427{ 428 register int i, j; 429 register union overhead *p; 430 int totfree = 0, 431 totused = 0; 432 433 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 434 for (i = 0; i < NBUCKETS; i++) { 435 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 436 ; 437 fprintf(stderr, " %d", j); 438 totfree += j * (1 << (i + 3)); 439 } 440 fprintf(stderr, "\nused:\t"); 441 for (i = 0; i < NBUCKETS; i++) { 442 fprintf(stderr, " %d", nmalloc[i]); 443 totused += nmalloc[i] * (1 << (i + 3)); 444 } 445 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", 446 totused, totfree); 447} 448#endif 449 450 451static int 452morepages(n) 453int n; 454{ 455 int fd = -1; 456 int offset; 457 458#ifdef NEED_DEV_ZERO 459 fd = open("/dev/zero", O_RDWR, 0); 460 if (fd == -1) 461 perror("/dev/zero"); 462#endif 463 464 if (pagepool_end - pagepool_start > pagesz) { 465 caddr_t addr = (caddr_t) 466 (((long)pagepool_start + pagesz - 1) & ~(pagesz - 1)); 467 if (munmap(addr, pagepool_end - addr) != 0) 468 warn("morepages: munmap %p", addr); 469 } 470 471 offset = (long)pagepool_start - ((long)pagepool_start & ~(pagesz - 1)); 472 473 if ((pagepool_start = mmap(0, n * pagesz, 474 PROT_READ|PROT_WRITE, 475 MAP_ANON|MAP_COPY, fd, 0)) == (caddr_t)-1) { 476 xprintf("Cannot map anonymous memory"); 477 return 0; 478 } 479 pagepool_end = pagepool_start + n * pagesz; 480 pagepool_start += offset; 481 482#ifdef NEED_DEV_ZERO 483 close(fd); 484#endif 485 return n; 486} 487