malloc.c revision 34192
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 1.2 1996/01/19 18:36:54 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, n; 160 register unsigned amt; 161 162 /* 163 * First time malloc is called, setup page size and 164 * align break pointer so all data will be page aligned. 165 */ 166 if (pagesz == 0) { 167 pagesz = n = getpagesize(); 168 if (morepages(NPOOLPAGES) == 0) 169 return NULL; 170 op = (union overhead *)(pagepool_start); 171 n = n - sizeof (*op) - ((int)op & (n - 1)); 172 if (n < 0) 173 n += pagesz; 174 if (n) { 175 pagepool_start += n; 176 } 177 bucket = 0; 178 amt = 8; 179 while (pagesz > amt) { 180 amt <<= 1; 181 bucket++; 182 } 183 pagebucket = bucket; 184 } 185 /* 186 * Convert amount of memory requested into closest block size 187 * stored in hash buckets which satisfies request. 188 * Account for space used per block for accounting. 189 */ 190 if (nbytes <= (n = pagesz - sizeof (*op) - RSLOP)) { 191#ifndef RCHECK 192 amt = 8; /* size of first bucket */ 193 bucket = 0; 194#else 195 amt = 16; /* size of first bucket */ 196 bucket = 1; 197#endif 198 n = -(sizeof (*op) + RSLOP); 199 } else { 200 amt = pagesz; 201 bucket = pagebucket; 202 } 203 while (nbytes > amt + n) { 204 amt <<= 1; 205 if (amt == 0) 206 return (NULL); 207 bucket++; 208 } 209 /* 210 * If nothing in hash bucket right now, 211 * request more memory from the system. 212 */ 213 if ((op = nextf[bucket]) == NULL) { 214 morecore(bucket); 215 if ((op = nextf[bucket]) == NULL) 216 return (NULL); 217 } 218 /* remove from linked list */ 219 nextf[bucket] = op->ov_next; 220 op->ov_magic = MAGIC; 221 op->ov_index = bucket; 222#ifdef MSTATS 223 nmalloc[bucket]++; 224#endif 225#ifdef RCHECK 226 /* 227 * Record allocated size of block and 228 * bound space with magic numbers. 229 */ 230 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 231 op->ov_rmagic = RMAGIC; 232 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 233#endif 234 return ((char *)(op + 1)); 235} 236 237/* 238 * Allocate more memory to the indicated bucket. 239 */ 240static void 241morecore(bucket) 242 int bucket; 243{ 244 register union overhead *op; 245 register int sz; /* size of desired block */ 246 int amt; /* amount to allocate */ 247 int nblks; /* how many blocks we get */ 248 249 /* 250 * sbrk_size <= 0 only for big, FLUFFY, requests (about 251 * 2^30 bytes on a VAX, I think) or for a negative arg. 252 */ 253 sz = 1 << (bucket + 3); 254#ifdef MALLOC_DEBUG 255 ASSERT(sz > 0); 256#else 257 if (sz <= 0) 258 return; 259#endif 260 if (sz < pagesz) { 261 amt = pagesz; 262 nblks = amt / sz; 263 } else { 264 amt = sz + pagesz; 265 nblks = 1; 266 } 267 if (amt > pagepool_end - pagepool_start) 268 if (morepages(amt/pagesz + NPOOLPAGES) == 0) 269 return; 270 op = (union overhead *)pagepool_start; 271 pagepool_start += amt; 272 273 /* 274 * Add new memory allocated to that on 275 * free list for this hash bucket. 276 */ 277 nextf[bucket] = op; 278 while (--nblks > 0) { 279 op->ov_next = (union overhead *)((caddr_t)op + sz); 280 op = (union overhead *)((caddr_t)op + sz); 281 } 282} 283 284void 285free(cp) 286 void *cp; 287{ 288 register int size; 289 register union overhead *op; 290 291 if (cp == NULL) 292 return; 293 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 294#ifdef MALLOC_DEBUG 295 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 296#else 297 if (op->ov_magic != MAGIC) 298 return; /* sanity */ 299#endif 300#ifdef RCHECK 301 ASSERT(op->ov_rmagic == RMAGIC); 302 ASSERT(*(u_short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC); 303#endif 304 size = op->ov_index; 305 ASSERT(size < NBUCKETS); 306 op->ov_next = nextf[size]; /* also clobbers ov_magic */ 307 nextf[size] = op; 308#ifdef MSTATS 309 nmalloc[size]--; 310#endif 311} 312 313/* 314 * When a program attempts "storage compaction" as mentioned in the 315 * old malloc man page, it realloc's an already freed block. Usually 316 * this is the last block it freed; occasionally it might be farther 317 * back. We have to search all the free lists for the block in order 318 * to determine its bucket: 1st we make one pass thru the lists 319 * checking only the first block in each; if that fails we search 320 * ``realloc_srchlen'' blocks in each list for a match (the variable 321 * is extern so the caller can modify it). If that fails we just copy 322 * however many bytes was given to realloc() and hope it's not huge. 323 */ 324int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ 325 326void * 327realloc(cp, nbytes) 328 void *cp; 329 size_t nbytes; 330{ 331 register u_int onb; 332 register int i; 333 union overhead *op; 334 char *res; 335 int was_alloced = 0; 336 337 if (cp == NULL) 338 return (malloc(nbytes)); 339 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 340 if (op->ov_magic == MAGIC) { 341 was_alloced++; 342 i = op->ov_index; 343 } else { 344 /* 345 * Already free, doing "compaction". 346 * 347 * Search for the old block of memory on the 348 * free list. First, check the most common 349 * case (last element free'd), then (this failing) 350 * the last ``realloc_srchlen'' items free'd. 351 * If all lookups fail, then assume the size of 352 * the memory block being realloc'd is the 353 * largest possible (so that all "nbytes" of new 354 * memory are copied into). Note that this could cause 355 * a memory fault if the old area was tiny, and the moon 356 * is gibbous. However, that is very unlikely. 357 */ 358 if ((i = findbucket(op, 1)) < 0 && 359 (i = findbucket(op, realloc_srchlen)) < 0) 360 i = NBUCKETS; 361 } 362 onb = 1 << (i + 3); 363 if (onb < pagesz) 364 onb -= sizeof (*op) + RSLOP; 365 else 366 onb += pagesz - sizeof (*op) - RSLOP; 367 /* avoid the copy if same size block */ 368 if (was_alloced) { 369 if (i) { 370 i = 1 << (i + 2); 371 if (i < pagesz) 372 i -= sizeof (*op) + RSLOP; 373 else 374 i += pagesz - sizeof (*op) - RSLOP; 375 } 376 if (nbytes <= onb && nbytes > i) { 377#ifdef RCHECK 378 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 379 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 380#endif 381 return(cp); 382 } else 383 free(cp); 384 } 385 if ((res = malloc(nbytes)) == NULL) 386 return (NULL); 387 if (cp != res) /* common optimization if "compacting" */ 388 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 389 return (res); 390} 391 392/* 393 * Search ``srchlen'' elements of each free list for a block whose 394 * header starts at ``freep''. If srchlen is -1 search the whole list. 395 * Return bucket number, or -1 if not found. 396 */ 397static int 398findbucket(freep, srchlen) 399 union overhead *freep; 400 int srchlen; 401{ 402 register union overhead *p; 403 register int i, j; 404 405 for (i = 0; i < NBUCKETS; i++) { 406 j = 0; 407 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { 408 if (p == freep) 409 return (i); 410 j++; 411 } 412 } 413 return (-1); 414} 415 416#ifdef MSTATS 417/* 418 * mstats - print out statistics about malloc 419 * 420 * Prints two lines of numbers, one showing the length of the free list 421 * for each size category, the second showing the number of mallocs - 422 * frees for each size category. 423 */ 424mstats(s) 425 char *s; 426{ 427 register int i, j; 428 register union overhead *p; 429 int totfree = 0, 430 totused = 0; 431 432 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 433 for (i = 0; i < NBUCKETS; i++) { 434 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 435 ; 436 fprintf(stderr, " %d", j); 437 totfree += j * (1 << (i + 3)); 438 } 439 fprintf(stderr, "\nused:\t"); 440 for (i = 0; i < NBUCKETS; i++) { 441 fprintf(stderr, " %d", nmalloc[i]); 442 totused += nmalloc[i] * (1 << (i + 3)); 443 } 444 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", 445 totused, totfree); 446} 447#endif 448 449 450static int 451morepages(n) 452int n; 453{ 454 int fd = -1; 455 int offset; 456 457#ifdef NEED_DEV_ZERO 458 fd = open("/dev/zero", O_RDWR, 0); 459 if (fd == -1) 460 perror("/dev/zero"); 461#endif 462 463 if (pagepool_end - pagepool_start > pagesz) { 464 caddr_t addr = (caddr_t) 465 (((int)pagepool_start + pagesz - 1) & ~(pagesz - 1)); 466 if (munmap(addr, pagepool_end - addr) != 0) 467 warn("morepages: munmap %p", addr); 468 } 469 470 offset = (int)pagepool_start - ((int)pagepool_start & ~(pagesz - 1)); 471 472 if ((pagepool_start = mmap(0, n * pagesz, 473 PROT_READ|PROT_WRITE, 474 MAP_ANON|MAP_COPY, fd, 0)) == (caddr_t)-1) { 475 xprintf("Cannot map anonymous memory"); 476 return 0; 477 } 478 pagepool_end = pagepool_start + n * pagesz; 479 pagepool_start += offset; 480 481#ifdef NEED_DEV_ZERO 482 close(fd); 483#endif 484 return n; 485} 486