1 /*- 2 * Copyright (c) 1983, 1991 The Regents of the University of California. 3 * All rights reserved. 4 * 5 * %sccs.include.redist.c% 6 */ 7 8 #ifndef lint 9 static char sccsid[] = "@(#)alloc.c 5.5 (Berkeley) 04/04/91"; 10 #endif /* not lint */ 11 12 /* From "@(#)malloc.c 5.5 (Berkeley) 2/25/86"; */ 13 14 /* 15 * malloc.c (Caltech) 2/21/82 16 * Chris Kingsley, kingsley@cit-20. 17 * 18 * This is a very fast storage allocator. It allocates blocks of a small 19 * number of different sizes, and keeps free lists of each size. Blocks that 20 * don't exactly fit are passed up to the next larger size. In this 21 * implementation, the available sizes are 2^n-4 (or 2^n-10) bytes long. 22 * This is designed for use in a virtual memory environment. 23 */ 24 25 #include <sys/types.h> 26 27 #define NULL 0 28 29 /* 30 * The overhead on a block is at least 4 bytes. When free, this space 31 * contains a pointer to the next free block, and the bottom two bits must 32 * be zero. When in use, the first byte is set to MAGIC, and the second 33 * byte is the size index. The remaining bytes are for alignment. 34 * If range checking is enabled then a second word holds the size of the 35 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC). 36 * The order of elements is critical: ov_magic must overlay the low order 37 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern. 38 */ 39 union overhead { 40 union overhead *ov_next; /* when free */ 41 struct { 42 u_char ovu_magic; /* magic number */ 43 u_char ovu_index; /* bucket # */ 44 #ifdef RCHECK 45 u_short ovu_rmagic; /* range magic number */ 46 u_int ovu_size; /* actual block size */ 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 /* 77 * nmalloc[i] is the difference between the number of mallocs and frees 78 * for a given block size. 79 */ 80 static u_int nmalloc[NBUCKETS]; 81 82 #if defined(DEBUG) || defined(RCHECK) 83 #define ASSERT(p) if (!(p)) botch("p") 84 static 85 botch(s) 86 char *s; 87 { 88 printf("\r\nassertion botched: %s\r\n", s); 89 abort(); 90 } 91 #else 92 #define ASSERT(p) 93 #endif 94 95 char * 96 malloc(nbytes) 97 unsigned nbytes; 98 { 99 register union overhead *op; 100 register int bucket; 101 register unsigned amt, n; 102 103 /* 104 * First time malloc is called, setup page size and 105 * align break pointer so all data will be page aligned. 106 */ 107 if (pagesz == 0) { 108 pagesz = n = getpagesize(); 109 op = (union overhead *)sbrk(0); 110 n = n - sizeof (*op) - ((int)op & (n - 1)); 111 if (n < 0) 112 n += pagesz; 113 if (n) { 114 if (sbrk(n) == (char *)-1) 115 return (NULL); 116 } 117 bucket = 0; 118 amt = 8; 119 while (pagesz > amt) { 120 amt <<= 1; 121 bucket++; 122 } 123 pagebucket = bucket; 124 } 125 /* 126 * Convert amount of memory requested into closest block size 127 * stored in hash buckets which satisfies request. 128 * Account for space used per block for accounting. 129 */ 130 if (nbytes <= (n = pagesz - sizeof (*op) - RSLOP)) { 131 #ifndef RCHECK 132 amt = 8; /* size of first bucket */ 133 bucket = 0; 134 #else 135 amt = 16; /* size of first bucket */ 136 bucket = 1; 137 #endif 138 n = -(sizeof (*op) + RSLOP); 139 } else { 140 amt = pagesz; 141 bucket = pagebucket; 142 } 143 while (nbytes > amt + n) { 144 amt <<= 1; 145 if (amt == 0) 146 return (NULL); 147 bucket++; 148 } 149 /* 150 * If nothing in hash bucket right now, 151 * request more memory from the system. 152 */ 153 if ((op = nextf[bucket]) == NULL) { 154 morecore(bucket); 155 if ((op = nextf[bucket]) == NULL) 156 return (NULL); 157 } 158 /* remove from linked list */ 159 nextf[bucket] = op->ov_next; 160 op->ov_magic = MAGIC; 161 op->ov_index = bucket; 162 nmalloc[bucket]++; 163 #ifdef RCHECK 164 /* 165 * Record allocated size of block and 166 * bound space with magic numbers. 167 */ 168 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1); 169 op->ov_rmagic = RMAGIC; 170 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC; 171 #endif 172 return ((char *)(op + 1)); 173 } 174 175 /* 176 * Allocate more memory to the indicated bucket. 177 */ 178 morecore(bucket) 179 int bucket; 180 { 181 register union overhead *op; 182 register int sz; /* size of desired block */ 183 int amt; /* amount to allocate */ 184 int nblks; /* how many blocks we get */ 185 186 /* 187 * sbrk_size <= 0 only for big, FLUFFY, requests (about 188 * 2^30 bytes on a VAX, I think) or for a negative arg. 189 */ 190 sz = 1 << (bucket + 3); 191 #ifdef DEBUG 192 ASSERT(sz > 0); 193 #else 194 if (sz <= 0) 195 return; 196 #endif 197 if (sz < pagesz) { 198 amt = pagesz; 199 nblks = amt / sz; 200 } else { 201 amt = sz + pagesz; 202 nblks = 1; 203 } 204 op = (union overhead *)sbrk(amt); 205 /* no more room! */ 206 if ((int)op == -1) 207 return; 208 /* 209 * Add new memory allocated to that on 210 * free list for this hash bucket. 211 */ 212 nextf[bucket] = op; 213 while (--nblks > 0) { 214 op->ov_next = (union overhead *)((caddr_t)op + sz); 215 op = (union overhead *)((caddr_t)op + sz); 216 } 217 } 218 219 free(cp) 220 char *cp; 221 { 222 register int size; 223 register union overhead *op; 224 225 if (cp == NULL) 226 return; 227 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 228 /* 229 * The following botch is because csh tries to free a free block 230 * when processing the =~ or !~ operators. -- layer@ucbmonet 231 */ 232 #ifdef CSHbotch /* was 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 nmalloc[size]--; 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 static int findbucket(); 272 273 if (cp == NULL) 274 return (malloc(nbytes)); 275 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 276 if (op->ov_magic == MAGIC) { 277 was_alloced++; 278 i = op->ov_index; 279 } else { 280 /* 281 * Already free, doing "compaction". 282 * 283 * Search for the old block of memory on the 284 * free list. First, check the most common 285 * case (last element free'd), then (this failing) 286 * the last ``realloc_srchlen'' items free'd. 287 * If all lookups fail, then assume the size of 288 * the memory block being realloc'd is the 289 * largest possible (so that all "nbytes" of new 290 * memory are copied into). Note that this could cause 291 * a memory fault if the old area was tiny, and the moon 292 * is gibbous. However, that is very unlikely. 293 */ 294 if ((i = findbucket(op, 1)) < 0 && 295 (i = findbucket(op, realloc_srchlen)) < 0) 296 i = NBUCKETS; 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 if "compacting" */ 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 /* 353 * mstats - print out statistics about malloc 354 * 355 * Prints two lines of numbers, one showing the length of the free list 356 * for each size category, the second showing the number of mallocs - 357 * frees for each size category. 358 */ 359 showall(s) 360 char **s; 361 { 362 register int i, j; 363 register union overhead *p; 364 int totfree = 0, 365 totused = 0; 366 367 if (s[1]) 368 printf("Memory allocation statistics %s\nfree:", s[1]); 369 for (i = 0; i < NBUCKETS; i++) { 370 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 371 ; 372 if (s[1]) 373 printf(" %d", j); 374 totfree += j * (1 << (i + 3)); 375 } 376 if (s[1]) 377 printf("\nused:"); 378 for (i = 0; i < NBUCKETS; i++) { 379 if (s[1]) 380 printf(" %d", nmalloc[i]); 381 totused += nmalloc[i] * (1 << (i + 3)); 382 } 383 if (s[1]) 384 printf("\n"); 385 printf("Total in use: %d, total free: %d\n", totused, totfree); 386 } 387