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 5.5 (Berkeley) 02/25/86"; 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-10) bytes long. 19 * This is designed for use in a virtual memory environment. 20 */ 21 22 #include <sys/types.h> 23 24 #define NULL 0 25 26 /* 27 * The overhead on a block is at least 4 bytes. When free, this space 28 * contains a pointer to the next free block, and the bottom two bits must 29 * be zero. When in use, the first byte is set to MAGIC, and the second 30 * byte is the size index. The remaining bytes are for alignment. 31 * If range checking is enabled then a second word holds the size of the 32 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC). 33 * The order of elements is critical: ov_magic must overlay the low order 34 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern. 35 */ 36 union overhead { 37 union overhead *ov_next; /* when free */ 38 struct { 39 u_char ovu_magic; /* magic number */ 40 u_char ovu_index; /* bucket # */ 41 #ifdef RCHECK 42 u_short ovu_rmagic; /* range magic number */ 43 u_int ovu_size; /* actual block size */ 44 #endif 45 } ovu; 46 #define ov_magic ovu.ovu_magic 47 #define ov_index ovu.ovu_index 48 #define ov_rmagic ovu.ovu_rmagic 49 #define ov_size ovu.ovu_size 50 }; 51 52 #define MAGIC 0xef /* magic # on accounting info */ 53 #define RMAGIC 0x5555 /* magic # on range info */ 54 55 #ifdef RCHECK 56 #define RSLOP sizeof (u_short) 57 #else 58 #define RSLOP 0 59 #endif 60 61 /* 62 * nextf[i] is the pointer to the next free block of size 2^(i+3). The 63 * smallest allocatable block is 8 bytes. The overhead information 64 * precedes the data area returned to the user. 65 */ 66 #define NBUCKETS 30 67 static union overhead *nextf[NBUCKETS]; 68 extern char *sbrk(); 69 70 static int pagesz; /* page size */ 71 static int pagebucket; /* page size bucket */ 72 73 #ifdef MSTATS 74 /* 75 * nmalloc[i] is the difference between the number of mallocs and frees 76 * for a given block size. 77 */ 78 static u_int nmalloc[NBUCKETS]; 79 #include <stdio.h> 80 #endif 81 82 #if defined(DEBUG) || defined(RCHECK) 83 #define ASSERT(p) if (!(p)) botch("p") 84 #include <stdio.h> 85 static 86 botch(s) 87 char *s; 88 { 89 fprintf(stderr, "\r\nassertion botched: %s\r\n", s); 90 (void) fflush(stderr); /* just in case user buffered it */ 91 abort(); 92 } 93 #else 94 #define ASSERT(p) 95 #endif 96 97 char * 98 malloc(nbytes) 99 unsigned nbytes; 100 { 101 register union overhead *op; 102 register int bucket; 103 register unsigned amt, n; 104 105 /* 106 * First time malloc is called, setup page size and 107 * align break pointer so all data will be page aligned. 108 */ 109 if (pagesz == 0) { 110 pagesz = n = getpagesize(); 111 op = (union overhead *)sbrk(0); 112 n = n - sizeof (*op) - ((int)op & (n - 1)); 113 if (n < 0) 114 n += pagesz; 115 if (n) { 116 if (sbrk(n) == (char *)-1) 117 return (NULL); 118 } 119 bucket = 0; 120 amt = 8; 121 while (pagesz > amt) { 122 amt <<= 1; 123 bucket++; 124 } 125 pagebucket = bucket; 126 } 127 /* 128 * Convert amount of memory requested into closest block size 129 * stored in hash buckets which satisfies request. 130 * Account for space used per block for accounting. 131 */ 132 if (nbytes <= (n = pagesz - sizeof (*op) - RSLOP)) { 133 #ifndef RCHECK 134 amt = 8; /* size of first bucket */ 135 bucket = 0; 136 #else 137 amt = 16; /* size of first bucket */ 138 bucket = 1; 139 #endif 140 n = -(sizeof (*op) + RSLOP); 141 } else { 142 amt = pagesz; 143 bucket = pagebucket; 144 } 145 while (nbytes > amt + n) { 146 amt <<= 1; 147 if (amt == 0) 148 return (NULL); 149 bucket++; 150 } 151 /* 152 * If nothing in hash bucket right now, 153 * request more memory from the system. 154 */ 155 if ((op = nextf[bucket]) == NULL) { 156 morecore(bucket); 157 if ((op = nextf[bucket]) == NULL) 158 return (NULL); 159 } 160 /* remove from linked list */ 161 nextf[bucket] = op->ov_next; 162 op->ov_magic = MAGIC; 163 op->ov_index = bucket; 164 #ifdef MSTATS 165 nmalloc[bucket]++; 166 #endif 167 #ifdef RCHECK 168 /* 169 * Record allocated size of block and 170 * bound space with magic numbers. 171 */ 172 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 173 op->ov_rmagic = RMAGIC; 174 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 175 #endif 176 return ((char *)(op + 1)); 177 } 178 179 /* 180 * Allocate more memory to the indicated bucket. 181 */ 182 morecore(bucket) 183 int bucket; 184 { 185 register union overhead *op; 186 register int sz; /* size of desired block */ 187 int amt; /* amount to allocate */ 188 int nblks; /* how many blocks we get */ 189 190 /* 191 * sbrk_size <= 0 only for big, FLUFFY, requests (about 192 * 2^30 bytes on a VAX, I think) or for a negative arg. 193 */ 194 sz = 1 << (bucket + 3); 195 #ifdef DEBUG 196 ASSERT(sz > 0); 197 #else 198 if (sz <= 0) 199 return; 200 #endif 201 if (sz < pagesz) { 202 amt = pagesz; 203 nblks = amt / sz; 204 } else { 205 amt = sz + pagesz; 206 nblks = 1; 207 } 208 op = (union overhead *)sbrk(amt); 209 /* no more room! */ 210 if ((int)op == -1) 211 return; 212 /* 213 * Add new memory allocated to that on 214 * free list for this hash bucket. 215 */ 216 nextf[bucket] = op; 217 while (--nblks > 0) { 218 op->ov_next = (union overhead *)((caddr_t)op + sz); 219 op = (union overhead *)((caddr_t)op + sz); 220 } 221 } 222 223 free(cp) 224 char *cp; 225 { 226 register int size; 227 register union overhead *op; 228 229 if (cp == NULL) 230 return; 231 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 232 #ifdef DEBUG 233 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 234 #else 235 if (op->ov_magic != MAGIC) 236 return; /* sanity */ 237 #endif 238 #ifdef RCHECK 239 ASSERT(op->ov_rmagic == RMAGIC); 240 ASSERT(*(u_short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC); 241 #endif 242 size = op->ov_index; 243 ASSERT(size < NBUCKETS); 244 op->ov_next = nextf[size]; /* also clobbers ov_magic */ 245 nextf[size] = op; 246 #ifdef MSTATS 247 nmalloc[size]--; 248 #endif 249 } 250 251 /* 252 * When a program attempts "storage compaction" as mentioned in the 253 * old malloc man page, it realloc's an already freed block. Usually 254 * this is the last block it freed; occasionally it might be farther 255 * back. We have to search all the free lists for the block in order 256 * to determine its bucket: 1st we make one pass thru the lists 257 * checking only the first block in each; if that fails we search 258 * ``realloc_srchlen'' blocks in each list for a match (the variable 259 * is extern so the caller can modify it). If that fails we just copy 260 * however many bytes was given to realloc() and hope it's not huge. 261 */ 262 int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ 263 264 char * 265 realloc(cp, nbytes) 266 char *cp; 267 unsigned nbytes; 268 { 269 register u_int onb, i; 270 union overhead *op; 271 char *res; 272 int was_alloced = 0; 273 274 if (cp == NULL) 275 return (malloc(nbytes)); 276 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 277 if (op->ov_magic == MAGIC) { 278 was_alloced++; 279 i = op->ov_index; 280 } else { 281 /* 282 * Already free, doing "compaction". 283 * 284 * Search for the old block of memory on the 285 * free list. First, check the most common 286 * case (last element free'd), then (this failing) 287 * the last ``realloc_srchlen'' items free'd. 288 * If all lookups fail, then assume the size of 289 * the memory block being realloc'd is the 290 * largest possible (so that all "nbytes" of new 291 * memory are copied into). Note that this could cause 292 * a memory fault if the old area was tiny, and the moon 293 * is gibbous. However, that is very unlikely. 294 */ 295 if ((i = findbucket(op, 1)) < 0 && 296 (i = findbucket(op, realloc_srchlen)) < 0) 297 i = NBUCKETS; 298 } 299 onb = 1 << (i + 3); 300 if (onb < pagesz) 301 onb -= sizeof (*op) + RSLOP; 302 else 303 onb += pagesz - sizeof (*op) - RSLOP; 304 /* avoid the copy if same size block */ 305 if (was_alloced) { 306 if (i) { 307 i = 1 << (i + 2); 308 if (i < pagesz) 309 i -= sizeof (*op) + RSLOP; 310 else 311 i += pagesz - sizeof (*op) - RSLOP; 312 } 313 if (nbytes <= onb && nbytes > i) { 314 #ifdef RCHECK 315 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 316 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 317 #endif 318 return(cp); 319 } else 320 free(cp); 321 } 322 if ((res = malloc(nbytes)) == NULL) 323 return (NULL); 324 if (cp != res) /* common optimization if "compacting" */ 325 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 326 return (res); 327 } 328 329 /* 330 * Search ``srchlen'' elements of each free list for a block whose 331 * header starts at ``freep''. If srchlen is -1 search the whole list. 332 * Return bucket number, or -1 if not found. 333 */ 334 static 335 findbucket(freep, srchlen) 336 union overhead *freep; 337 int srchlen; 338 { 339 register union overhead *p; 340 register int i, j; 341 342 for (i = 0; i < NBUCKETS; i++) { 343 j = 0; 344 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { 345 if (p == freep) 346 return (i); 347 j++; 348 } 349 } 350 return (-1); 351 } 352 353 #ifdef MSTATS 354 /* 355 * mstats - print out statistics about malloc 356 * 357 * Prints two lines of numbers, one showing the length of the free list 358 * for each size category, the second showing the number of mallocs - 359 * frees for each size category. 360 */ 361 mstats(s) 362 char *s; 363 { 364 register int i, j; 365 register union overhead *p; 366 int totfree = 0, 367 totused = 0; 368 369 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 370 for (i = 0; i < NBUCKETS; i++) { 371 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 372 ; 373 fprintf(stderr, " %d", j); 374 totfree += j * (1 << (i + 3)); 375 } 376 fprintf(stderr, "\nused:\t"); 377 for (i = 0; i < NBUCKETS; i++) { 378 fprintf(stderr, " %d", nmalloc[i]); 379 totused += nmalloc[i] * (1 << (i + 3)); 380 } 381 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", 382 totused, totfree); 383 } 384 #endif 385