1 /* 2 * Copyright (c) 1983 Regents of the University of California. 3 * All rights reserved. The Berkeley software License Agreement 4 * specifies the terms and conditions for redistribution. 5 */ 6 7 #ifndef lint 8 static char sccsid[] = "@(#)malloc.c 5.3 (Berkeley) 01/09/86"; 9 #endif not lint 10 11 /* 12 * malloc.c (Caltech) 2/21/82 13 * Chris Kingsley, kingsley@cit-20. 14 * 15 * This is a very fast storage allocator. It allocates blocks of a small 16 * number of different sizes, and keeps free lists of each size. Blocks that 17 * don't exactly fit are passed up to the next larger size. In this 18 * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long. 19 * This is designed for use in a program that uses vast quantities of memory, 20 * but bombs when it runs out. 21 */ 22 23 #include <sys/types.h> 24 25 #define NULL 0 26 27 /* 28 * The overhead on a block is at least 4 bytes. When free, this space 29 * contains a pointer to the next free block, and the bottom two bits must 30 * be zero. When in use, the first byte is set to MAGIC, and the second 31 * byte is the size index. The remaining bytes are for alignment. 32 * If range checking is enabled and the size of the block fits 33 * in two bytes, then the top two bytes hold the size of the requested block 34 * plus the range checking words, and the header word MINUS ONE. 35 */ 36 union overhead { 37 union overhead *ov_next; /* when free */ 38 struct { 39 #ifndef RCHECK 40 u_char ovu_magic; /* magic number */ 41 u_char ovu_index; /* bucket # */ 42 #else 43 u_int ovu_size; /* actual block size */ 44 u_char ovu_magic; /* magic number */ 45 u_char ovu_index; /* bucket # */ 46 u_short ovu_rmagic; /* range magic number */ 47 #endif 48 } ovu; 49 #define ov_magic ovu.ovu_magic 50 #define ov_index ovu.ovu_index 51 #define ov_rmagic ovu.ovu_rmagic 52 #define ov_size ovu.ovu_size 53 }; 54 55 #define MAGIC 0xef /* magic # on accounting info */ 56 #define RMAGIC 0x5555 /* magic # on range info */ 57 58 #ifdef RCHECK 59 #define RSLOP sizeof (u_short) 60 #else 61 #define RSLOP 0 62 #endif 63 64 /* 65 * nextf[i] is the pointer to the next free block of size 2^(i+3). The 66 * smallest allocatable block is 8 bytes. The overhead information 67 * precedes the data area returned to the user. 68 */ 69 #define NBUCKETS 30 70 static union overhead *nextf[NBUCKETS]; 71 extern char *sbrk(); 72 73 static int pagesz; /* page size */ 74 static int pagebucket; /* page size bucket */ 75 76 #ifdef MSTATS 77 /* 78 * nmalloc[i] is the difference between the number of mallocs and frees 79 * for a given block size. 80 */ 81 static u_int nmalloc[NBUCKETS]; 82 #include <stdio.h> 83 #endif 84 85 #ifdef DEBUG 86 #define ASSERT(p) if (!(p)) botch("p") 87 static 88 botch(s) 89 char *s; 90 { 91 92 printf("assertion botched: %s\n", s); 93 abort(); 94 } 95 #else 96 #define ASSERT(p) 97 #endif 98 99 char * 100 malloc(nbytes) 101 unsigned nbytes; 102 { 103 register union overhead *op; 104 register int bucket; 105 register unsigned amt, n; 106 107 /* 108 * First time malloc is called, setup page size and 109 * align break pointer so all data will be page aligned. 110 */ 111 if (pagesz == 0) { 112 pagesz = n = getpagesize(); 113 op = (union overhead *)sbrk(0); 114 n = n - sizeof (*op) - ((int)op & (n - 1)); 115 if (n < 0) 116 n += pagesz; 117 if (n) { 118 if (sbrk(n) == (char *)-1) 119 return (NULL); 120 } 121 bucket = 0; 122 amt = 8; 123 while (pagesz > amt) { 124 amt <<= 1; 125 bucket++; 126 } 127 pagebucket = bucket; 128 } 129 /* 130 * Convert amount of memory requested into closest block size 131 * stored in hash buckets which satisfies request. 132 * Account for space used per block for accounting. 133 */ 134 if (nbytes <= (n = pagesz - sizeof (*op) - RSLOP)) { 135 #ifndef RCHECK 136 amt = 8; /* size of first bucket */ 137 bucket = 0; 138 #else 139 amt = 16; /* size of first bucket */ 140 bucket = 1; 141 #endif 142 n = -(sizeof (*op) + RSLOP); 143 } else { 144 amt = pagesz; 145 bucket = pagebucket; 146 } 147 while (nbytes > amt + n) { 148 amt <<= 1; 149 if (amt == 0) 150 return (NULL); 151 bucket++; 152 } 153 /* 154 * If nothing in hash bucket right now, 155 * request more memory from the system. 156 */ 157 if ((op = nextf[bucket]) == NULL) { 158 morecore(bucket); 159 if ((op = nextf[bucket]) == NULL) 160 return (NULL); 161 } 162 /* remove from linked list */ 163 nextf[bucket] = op->ov_next; 164 op->ov_magic = MAGIC; 165 op->ov_index = bucket; 166 #ifdef MSTATS 167 nmalloc[bucket]++; 168 #endif 169 #ifdef RCHECK 170 /* 171 * Record allocated size of block and 172 * bound space with magic numbers. 173 */ 174 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 175 op->ov_rmagic = RMAGIC; 176 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 177 #endif 178 return ((char *)(op + 1)); 179 } 180 181 /* 182 * Allocate more memory to the indicated bucket. 183 */ 184 morecore(bucket) 185 int bucket; 186 { 187 register union overhead *op; 188 register int sz; /* size of desired block */ 189 int amt; /* amount to allocate */ 190 int nblks; /* how many blocks we get */ 191 192 /* 193 * sbrk_size <= 0 only for big, FLUFFY, requests (about 194 * 2^30 bytes on a VAX, I think) or for a negative arg. 195 */ 196 sz = 1 << (bucket + 3); 197 if (sz <= 0) 198 return; 199 if (sz < pagesz) { 200 amt = pagesz; 201 nblks = amt / sz; 202 } else { 203 amt = sz + pagesz; 204 nblks = 1; 205 } 206 op = (union overhead *)sbrk(amt); 207 /* no more room! */ 208 if ((int)op == -1) 209 return; 210 /* 211 * Add new memory allocated to that on 212 * free list for this hash bucket. 213 */ 214 nextf[bucket] = op; 215 while (--nblks > 0) { 216 op->ov_next = (union overhead *)((caddr_t)op + sz); 217 op = (union overhead *)((caddr_t)op + sz); 218 } 219 } 220 221 free(cp) 222 char *cp; 223 { 224 register int size; 225 register union overhead *op; 226 227 if (cp == NULL) 228 return; 229 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 230 #ifdef DEBUG 231 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 232 #else 233 if (op->ov_magic != MAGIC) 234 return; /* sanity */ 235 #endif 236 #ifdef RCHECK 237 ASSERT(op->ov_rmagic == RMAGIC); 238 ASSERT(*(u_short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC); 239 #endif 240 size = op->ov_index; 241 ASSERT(size < NBUCKETS); 242 op->ov_next = nextf[size]; 243 nextf[size] = op; 244 #ifdef MSTATS 245 nmalloc[size]--; 246 #endif 247 } 248 249 /* 250 * When a program attempts "storage compaction" as mentioned in the 251 * old malloc man page, it realloc's an already freed block. Usually 252 * this is the last block it freed; occasionally it might be farther 253 * back. We have to search all the free lists for the block in order 254 * to determine its bucket: 1st we make one pass thru the lists 255 * checking only the first block in each; if that fails we search 256 * ``realloc_srchlen'' blocks in each list for a match (the variable 257 * is extern so the caller can modify it). If that fails we just copy 258 * however many bytes was given to realloc() and hope it's not huge. 259 */ 260 int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ 261 262 char * 263 realloc(cp, nbytes) 264 char *cp; 265 unsigned nbytes; 266 { 267 register u_int onb, i; 268 union overhead *op; 269 char *res; 270 int was_alloced = 0; 271 272 if (cp == NULL) 273 return (malloc(nbytes)); 274 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 275 if (op->ov_magic == MAGIC) { 276 was_alloced++; 277 i = op->ov_index; 278 } else { 279 /* 280 * Already free, doing "compaction". 281 * 282 * Search for the old block of memory on the 283 * free list. First, check the most common 284 * case (last element free'd), then (this failing) 285 * the last ``realloc_srchlen'' items free'd. 286 * If all lookups fail, then assume the size of 287 * the memory block being realloc'd is the 288 * smallest possible. 289 */ 290 if ((i = findbucket(op, 1)) < 0 && 291 (i = findbucket(op, realloc_srchlen)) < 0) 292 #ifndef RCHECK 293 i = 0; 294 #else 295 i = 1; /* smallest possible w/ RCHECK */ 296 #endif 297 } 298 onb = 1 << (i + 3); 299 if (onb < pagesz) 300 onb -= sizeof (*op) + RSLOP; 301 else 302 onb += pagesz - sizeof (*op) - RSLOP; 303 /* avoid the copy if same size block */ 304 if (was_alloced) { 305 if (i) { 306 i = 1 << (i + 2); 307 if (i < pagesz) 308 i -= sizeof (*op) + RSLOP; 309 else 310 i += pagesz - sizeof (*op) - RSLOP; 311 } 312 if (nbytes <= onb && nbytes > i) { 313 #ifdef RCHECK 314 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 315 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 316 #endif 317 return(cp); 318 } else 319 free(cp); 320 } 321 if ((res = malloc(nbytes)) == NULL) 322 return (NULL); 323 if (cp != res) /* common optimization */ 324 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 325 return (res); 326 } 327 328 /* 329 * Search ``srchlen'' elements of each free list for a block whose 330 * header starts at ``freep''. If srchlen is -1 search the whole list. 331 * Return bucket number, or -1 if not found. 332 */ 333 static 334 findbucket(freep, srchlen) 335 union overhead *freep; 336 int srchlen; 337 { 338 register union overhead *p; 339 register int i, j; 340 341 for (i = 0; i < NBUCKETS; i++) { 342 j = 0; 343 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { 344 if (p == freep) 345 return (i); 346 j++; 347 } 348 } 349 return (-1); 350 } 351 352 #ifdef MSTATS 353 /* 354 * mstats - print out statistics about malloc 355 * 356 * Prints two lines of numbers, one showing the length of the free list 357 * for each size category, the second showing the number of mallocs - 358 * frees for each size category. 359 */ 360 mstats(s) 361 char *s; 362 { 363 register int i, j; 364 register union overhead *p; 365 int totfree = 0, 366 totused = 0; 367 368 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 369 for (i = 0; i < NBUCKETS; i++) { 370 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 371 ; 372 fprintf(stderr, " %d", j); 373 totfree += j * (1 << (i + 3)); 374 } 375 fprintf(stderr, "\nused:\t"); 376 for (i = 0; i < NBUCKETS; i++) { 377 fprintf(stderr, " %d", nmalloc[i]); 378 totused += nmalloc[i] * (1 << (i + 3)); 379 } 380 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", 381 totused, totfree); 382 } 383 #endif 384