1 #ifndef lint 2 static char sccsid[] = "@(#)malloc.c 4.2 (Berkeley) 09/11/83"; 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 printf("assertion botched: %s\n",s); 79 abort(); 80 } 81 #else 82 #define ASSERT(p) 83 #endif 84 85 char * 86 malloc(nbytes) 87 register unsigned nbytes; 88 { 89 register union overhead *p; 90 register int bucket = 0; 91 register unsigned shiftr; 92 93 /* 94 * Convert amount of memory requested into 95 * closest block size stored in hash buckets 96 * which satisfies request. Account for 97 * space used per block for accounting. 98 */ 99 nbytes += sizeof (union overhead) + RSLOP; 100 nbytes = (nbytes + 3) &~ 3; 101 shiftr = (nbytes - 1) >> 2; 102 /* apart from this loop, this is O(1) */ 103 while (shiftr >>= 1) 104 bucket++; 105 /* 106 * If nothing in hash bucket right now, 107 * request more memory from the system. 108 */ 109 if (nextf[bucket] == NULL) 110 morecore(bucket); 111 if ((p = (union overhead *)nextf[bucket]) == NULL) 112 return (NULL); 113 /* remove from linked list */ 114 nextf[bucket] = nextf[bucket]->ov_next; 115 p->ov_magic = MAGIC; 116 p->ov_index= bucket; 117 #ifdef MSTATS 118 nmalloc[bucket]++; 119 #endif 120 #ifdef RCHECK 121 /* 122 * Record allocated size of block and 123 * bound space with magic numbers. 124 */ 125 if (nbytes <= 0x10000) 126 p->ov_size = nbytes - 1; 127 p->ov_rmagic = RMAGIC; 128 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; 129 #endif 130 return ((char *)(p + 1)); 131 } 132 133 /* 134 * Allocate more memory to the indicated bucket. 135 */ 136 static 137 morecore(bucket) 138 register bucket; 139 { 140 register union overhead *op; 141 register int rnu; /* 2^rnu bytes will be requested */ 142 register int nblks; /* become nblks blocks of the desired size */ 143 register int siz; 144 145 if (nextf[bucket]) 146 return; 147 /* 148 * Insure memory is allocated 149 * on a page boundary. Should 150 * make getpageize call? 151 */ 152 op = (union overhead *)sbrk(0); 153 if ((int)op & 0x3ff) 154 sbrk(1024 - ((int)op & 0x3ff)); 155 /* take 2k unless the block is bigger than that */ 156 rnu = (bucket <= 8) ? 11 : bucket + 3; 157 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ 158 if (rnu < bucket) 159 rnu = bucket; 160 op = (union overhead *)sbrk(1 << rnu); 161 /* no more room! */ 162 if ((int)op == -1) 163 return; 164 /* 165 * Round up to minimum allocation size boundary 166 * and deduct from block count to reflect. 167 */ 168 if ((int)op & 7) { 169 op = (union overhead *)(((int)op + 8) &~ 7); 170 nblks--; 171 } 172 /* 173 * Add new memory allocated to that on 174 * free list for this hash bucket. 175 */ 176 nextf[bucket] = op; 177 siz = 1 << (bucket + 3); 178 while (--nblks > 0) { 179 op->ov_next = (union overhead *)((caddr_t)op + siz); 180 op = (union overhead *)((caddr_t)op + siz); 181 } 182 } 183 184 free(cp) 185 char *cp; 186 { 187 register int size; 188 register union overhead *op; 189 190 if (cp == NULL) 191 return; 192 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 193 #ifdef debug 194 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 195 #else 196 if (op->ov_magic != MAGIC) 197 return; /* sanity */ 198 #endif 199 #ifdef RCHECK 200 ASSERT(op->ov_rmagic == RMAGIC); 201 if (op->ov_index <= 13) 202 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC); 203 #endif 204 ASSERT(op->ov_index < NBUCKETS); 205 size = op->ov_index; 206 op->ov_next = nextf[size]; 207 nextf[size] = op; 208 #ifdef MSTATS 209 nmalloc[size]--; 210 #endif 211 } 212 213 /* 214 * When a program attempts "storage compaction" as mentioned in the 215 * old malloc man page, it realloc's an already freed block. Usually 216 * this is the last block it freed; occasionally it might be farther 217 * back. We have to search all the free lists for the block in order 218 * to determine its bucket: 1st we make one pass thru the lists 219 * checking only the first block in each; if that fails we search 220 * ``realloc_srchlen'' blocks in each list for a match (the variable 221 * is extern so the caller can modify it). If that fails we just copy 222 * however many bytes was given to realloc() and hope it's not huge. 223 */ 224 int realloc_srchlen = 4; /* 4 should be plenty. -1 means whole list */ 225 226 char * 227 realloc(cp, nbytes) 228 char *cp; 229 unsigned nbytes; 230 { 231 register u_int onb; 232 union overhead *op; 233 char *res; 234 register int i; 235 int was_alloced = 0; 236 237 if (cp == NULL) 238 return (malloc(nbytes)); 239 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 240 if (op->ov_magic == MAGIC) { 241 was_alloced++; 242 i = op->ov_index; 243 } 244 else { /* already free: he is doing "compaction" (tee hee) */ 245 if ((i = findbucket(op, 1)) < 0 && 246 (i = findbucket(op, realloc_srchlen)) < 0) 247 i = 0; /* assume shortest possible */ 248 } 249 onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; 250 if (was_alloced && /* avoid the copy if same size block */ 251 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) 252 return(cp); 253 if ((res = malloc(nbytes)) == NULL) 254 return (NULL); 255 if (cp != res) /* common optimization */ 256 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 257 if (was_alloced) 258 free(cp); 259 return (res); 260 } 261 262 /* 263 * Search ``srchlen'' elements of each free list for a block whose 264 * header starts at ``freep''. If srchlen is -1 search the whole list. 265 * Return bucket number, or -1 if not found. 266 */ 267 static 268 findbucket(freep, srchlen) 269 union overhead *freep; 270 int srchlen; 271 { 272 register union overhead *p; 273 register int i, j; 274 275 for (i = 0; i < NBUCKETS; i++) 276 for (j = 0, p = nextf[i]; p && j != srchlen; j++, p = p->ov_next) 277 if (p == freep) 278 return (i); 279 return (-1); 280 } 281 282 #ifdef MSTATS 283 /* 284 * mstats - print out statistics about malloc 285 * 286 * Prints two lines of numbers, one showing the length of the free list 287 * for each size category, the second showing the number of mallocs - 288 * frees for each size category. 289 */ 290 mstats(s) 291 char *s; 292 { 293 register int i, j; 294 register union overhead *p; 295 int totfree = 0, 296 totused = 0; 297 298 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s); 299 for (i = 0; i < NBUCKETS; i++) { 300 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 301 ; 302 fprintf(stderr, " %d", j); 303 totfree += j * (1 << (i + 3)); 304 } 305 fprintf(stderr, "\nused:\t"); 306 for (i = 0; i < NBUCKETS; i++) { 307 fprintf(stderr, " %d", nmalloc[i]); 308 totused += nmalloc[i] * (1 << (i + 3)); 309 } 310 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n", totused, totfree); 311 } 312 #endif 313