1 #ifndef lint 2 static char sccsid[] = "@(#)malloc.c 4.3 (Berkeley) 09/16/83"; 3 #endif 4 5 /* 6 * malloc.c (Caltech) 2/21/82 7 * Chris Kingsley, kingsley@cit-20. 8 * 9 * This is a very fast storage allocator. It allocates blocks of a small 10 * number of different sizes, and keeps free lists of each size. Blocks that 11 * don't exactly fit are passed up to the next larger size. In this 12 * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long. 13 * This is designed for use in a program that uses vast quantities of memory, 14 * but bombs when it runs out. 15 */ 16 17 #include <sys/types.h> 18 19 #define NULL 0 20 21 /* 22 * The overhead on a block is at least 4 bytes. When free, this space 23 * contains a pointer to the next free block, and the bottom two bits must 24 * be zero. When in use, the first byte is set to MAGIC, and the second 25 * byte is the size index. The remaining bytes are for alignment. 26 * If range checking is enabled and the size of the block fits 27 * in two bytes, then the top two bytes hold the size of the requested block 28 * plus the range checking words, and the header word MINUS ONE. 29 */ 30 union overhead { 31 union overhead *ov_next; /* when free */ 32 struct { 33 u_char ovu_magic; /* magic number */ 34 u_char ovu_index; /* bucket # */ 35 #ifdef RCHECK 36 u_short ovu_size; /* actual block size */ 37 u_int ovu_rmagic; /* range magic number */ 38 #endif 39 } ovu; 40 #define ov_magic ovu.ovu_magic 41 #define ov_index ovu.ovu_index 42 #define ov_size ovu.ovu_size 43 #define ov_rmagic ovu.ovu_rmagic 44 }; 45 46 #define MAGIC 0xff /* magic # on accounting info */ 47 #define RMAGIC 0x55555555 /* magic # on range info */ 48 #ifdef RCHECK 49 #define RSLOP sizeof (u_int) 50 #else 51 #define RSLOP 0 52 #endif 53 54 /* 55 * nextf[i] is the pointer to the next free block of size 2^(i+3). The 56 * smallest allocatable block is 8 bytes. The overhead information 57 * precedes the data area returned to the user. 58 */ 59 #define NBUCKETS 30 60 static union overhead *nextf[NBUCKETS]; 61 extern char *sbrk(); 62 63 #ifdef MSTATS 64 /* 65 * nmalloc[i] is the difference between the number of mallocs and frees 66 * for a given block size. 67 */ 68 static u_int nmalloc[NBUCKETS]; 69 #include <stdio.h> 70 #endif 71 72 #ifdef debug 73 #define ASSERT(p) if (!(p)) botch("p"); else 74 static 75 botch(s) 76 char *s; 77 { 78 79 printf("assertion botched: %s\n", s); 80 abort(); 81 } 82 #else 83 #define ASSERT(p) 84 #endif 85 86 char * 87 malloc(nbytes) 88 register unsigned nbytes; 89 { 90 register union overhead *p; 91 register int bucket = 0; 92 register unsigned shiftr; 93 94 /* 95 * Convert amount of memory requested into 96 * closest block size stored in hash buckets 97 * which satisfies request. Account for 98 * space used per block for accounting. 99 */ 100 nbytes += sizeof (union overhead) + RSLOP; 101 nbytes = (nbytes + 3) &~ 3; 102 shiftr = (nbytes - 1) >> 2; 103 /* apart from this loop, this is O(1) */ 104 while (shiftr >>= 1) 105 bucket++; 106 /* 107 * If nothing in hash bucket right now, 108 * request more memory from the system. 109 */ 110 if (nextf[bucket] == NULL) 111 morecore(bucket); 112 if ((p = (union overhead *)nextf[bucket]) == NULL) 113 return (NULL); 114 /* remove from linked list */ 115 nextf[bucket] = nextf[bucket]->ov_next; 116 p->ov_magic = MAGIC; 117 p->ov_index= bucket; 118 #ifdef MSTATS 119 nmalloc[bucket]++; 120 #endif 121 #ifdef RCHECK 122 /* 123 * Record allocated size of block and 124 * bound space with magic numbers. 125 */ 126 if (nbytes <= 0x10000) 127 p->ov_size = nbytes - 1; 128 p->ov_rmagic = RMAGIC; 129 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; 130 #endif 131 return ((char *)(p + 1)); 132 } 133 134 /* 135 * Allocate more memory to the indicated bucket. 136 */ 137 static 138 morecore(bucket) 139 register bucket; 140 { 141 register union overhead *op; 142 register int rnu; /* 2^rnu bytes will be requested */ 143 register int nblks; /* become nblks blocks of the desired size */ 144 register int siz; 145 146 if (nextf[bucket]) 147 return; 148 /* 149 * Insure memory is allocated 150 * on a page boundary. Should 151 * make getpageize call? 152 */ 153 op = (union overhead *)sbrk(0); 154 if ((int)op & 0x3ff) 155 sbrk(1024 - ((int)op & 0x3ff)); 156 /* take 2k unless the block is bigger than that */ 157 rnu = (bucket <= 8) ? 11 : bucket + 3; 158 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ 159 if (rnu < bucket) 160 rnu = bucket; 161 op = (union overhead *)sbrk(1 << rnu); 162 /* no more room! */ 163 if ((int)op == -1) 164 return; 165 /* 166 * Round up to minimum allocation size boundary 167 * and deduct from block count to reflect. 168 */ 169 if ((int)op & 7) { 170 op = (union overhead *)(((int)op + 8) &~ 7); 171 nblks--; 172 } 173 /* 174 * Add new memory allocated to that on 175 * free list for this hash bucket. 176 */ 177 nextf[bucket] = op; 178 siz = 1 << (bucket + 3); 179 while (--nblks > 0) { 180 op->ov_next = (union overhead *)((caddr_t)op + siz); 181 op = (union overhead *)((caddr_t)op + siz); 182 } 183 } 184 185 free(cp) 186 char *cp; 187 { 188 register int size; 189 register union overhead *op; 190 191 if (cp == NULL) 192 return; 193 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 194 #ifdef debug 195 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 196 #else 197 if (op->ov_magic != MAGIC) 198 return; /* sanity */ 199 #endif 200 #ifdef RCHECK 201 ASSERT(op->ov_rmagic == RMAGIC); 202 if (op->ov_index <= 13) 203 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC); 204 #endif 205 ASSERT(op->ov_index < NBUCKETS); 206 size = op->ov_index; 207 op->ov_next = nextf[size]; 208 nextf[size] = op; 209 #ifdef MSTATS 210 nmalloc[size]--; 211 #endif 212 } 213 214 /* 215 * When a program attempts "storage compaction" as mentioned in the 216 * old malloc man page, it realloc's an already freed block. Usually 217 * this is the last block it freed; occasionally it might be farther 218 * back. We have to search all the free lists for the block in order 219 * to determine its bucket: 1st we make one pass thru the lists 220 * checking only the first block in each; if that fails we search 221 * ``realloc_srchlen'' blocks in each list for a match (the variable 222 * is extern so the caller can modify it). If that fails we just copy 223 * however many bytes was given to realloc() and hope it's not huge. 224 */ 225 int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */ 226 227 char * 228 realloc(cp, nbytes) 229 char *cp; 230 unsigned nbytes; 231 { 232 register u_int onb; 233 union overhead *op; 234 char *res; 235 register int i; 236 int was_alloced = 0; 237 238 if (cp == NULL) 239 return (malloc(nbytes)); 240 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 241 if (op->ov_magic == MAGIC) { 242 was_alloced++; 243 i = op->ov_index; 244 } else { 245 /* 246 * Already free, doing "compaction". 247 * 248 * Search for the old block of memory on the 249 * free list. First, check the most common 250 * case (last element free'd), then (this failing) 251 * the last ``realloc_srchlen'' items free'd. 252 * If all lookups fail, then assume the size of 253 * the memory block being realloc'd is the 254 * smallest possible. 255 */ 256 if ((i = findbucket(op, 1)) < 0 && 257 (i = findbucket(op, realloc_srchlen)) < 0) 258 i = 0; 259 } 260 onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; 261 /* avoid the copy if same size block */ 262 if (was_alloced && 263 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) 264 return(cp); 265 if ((res = malloc(nbytes)) == NULL) 266 return (NULL); 267 if (cp != res) /* common optimization */ 268 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 269 if (was_alloced) 270 free(cp); 271 return (res); 272 } 273 274 /* 275 * Search ``srchlen'' elements of each free list for a block whose 276 * header starts at ``freep''. If srchlen is -1 search the whole list. 277 * Return bucket number, or -1 if not found. 278 */ 279 static 280 findbucket(freep, srchlen) 281 union overhead *freep; 282 int srchlen; 283 { 284 register union overhead *p; 285 register int i, j; 286 287 for (i = 0; i < NBUCKETS; i++) { 288 j = 0; 289 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) { 290 if (p == freep) 291 return (i); 292 j++; 293 } 294 } 295 return (-1); 296 } 297 298 #ifdef MSTATS 299 /* 300 * mstats - print out statistics about malloc 301 * 302 * Prints two lines of numbers, one showing the length of the free list 303 * for each size category, the second showing the number of mallocs - 304 * frees for each size category. 305 */ 306 mstats(s) 307 char *s; 308 { 309 register int i, j; 310 register union overhead *p; 311 int totfree = 0, 312 totused = 0; 313 314 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 315 for (i = 0; i < NBUCKETS; i++) { 316 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 317 ; 318 fprintf(stderr, " %d", j); 319 totfree += j * (1 << (i + 3)); 320 } 321 fprintf(stderr, "\nused:\t"); 322 for (i = 0; i < NBUCKETS; i++) { 323 fprintf(stderr, " %d", nmalloc[i]); 324 totused += nmalloc[i] * (1 << (i + 3)); 325 } 326 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", 327 totused, totfree); 328 } 329 #endif 330