1 #ifndef lint 2 static char *sccsid = "@(#)alloc.c 4.3 (Berkeley from Caltech) 11/13/83"; 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 debug 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 #endif 70 71 #ifdef debug 72 #define ASSERT(p) if (!(p)) botch("p"); else 73 static 74 botch(s) 75 char *s; 76 { 77 printf("assertion botched: %s\n",s); 78 abort(); 79 } 80 #else 81 #define ASSERT(p) 82 #endif 83 84 char * 85 malloc(nbytes) 86 register unsigned nbytes; 87 { 88 register union overhead *p; 89 register int bucket = 0; 90 register unsigned shiftr; 91 92 /* 93 * Convert amount of memory requested into 94 * closest block size stored in hash buckets 95 * which satisfies request. Account for 96 * space used per block for accounting. 97 */ 98 nbytes += sizeof (union overhead) + RSLOP; 99 nbytes = (nbytes + 3) &~ 3; 100 shiftr = (nbytes - 1) >> 2; 101 /* apart from this loop, this is O(1) */ 102 while (shiftr >>= 1) 103 bucket++; 104 /* 105 * If nothing in hash bucket right now, 106 * request more memory from the system. 107 */ 108 if (nextf[bucket] == NULL) 109 morecore(bucket); 110 if ((p = (union overhead *)nextf[bucket]) == NULL) 111 return (NULL); 112 /* remove from linked list */ 113 nextf[bucket] = nextf[bucket]->ov_next; 114 p->ov_magic = MAGIC; 115 p->ov_index= bucket; 116 #ifdef debug 117 nmalloc[bucket]++; 118 #endif 119 #ifdef RCHECK 120 /* 121 * Record allocated size of block and 122 * bound space with magic numbers. 123 */ 124 if (nbytes <= 0x10000) 125 p->ov_size = nbytes - 1; 126 p->ov_rmagic = RMAGIC; 127 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; 128 #endif 129 return ((char *)(p + 1)); 130 } 131 132 /* 133 * Allocate more memory to the indicated bucket. 134 */ 135 static 136 morecore(bucket) 137 register bucket; 138 { 139 register union overhead *op; 140 register int rnu; /* 2^rnu bytes will be requested */ 141 register int nblks; /* become nblks blocks of the desired size */ 142 register int siz; 143 144 if (nextf[bucket]) 145 return; 146 /* 147 * Insure memory is allocated 148 * on a page boundary. Should 149 * make getpageize call? 150 */ 151 op = (union overhead *)sbrk(0); 152 if ((int)op & 0x3ff) 153 sbrk(1024 - ((int)op & 0x3ff)); 154 /* take 2k unless the block is bigger than that */ 155 rnu = (bucket <= 8) ? 11 : bucket + 3; 156 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ 157 if (rnu < bucket) 158 rnu = bucket; 159 op = (union overhead *)sbrk(1 << rnu); 160 /* no more room! */ 161 if ((int)op == -1) 162 return; 163 /* 164 * Round up to minimum allocation size boundary 165 * and deduct from block count to reflect. 166 */ 167 if ((int)op & 7) { 168 op = (union overhead *)(((int)op + 8) &~ 7); 169 nblks--; 170 } 171 /* 172 * Add new memory allocated to that on 173 * free list for this hash bucket. 174 */ 175 nextf[bucket] = op; 176 siz = 1 << (bucket + 3); 177 while (--nblks > 0) { 178 op->ov_next = (union overhead *)((caddr_t)op + siz); 179 op = (union overhead *)((caddr_t)op + siz); 180 } 181 } 182 183 free(cp) 184 char *cp; 185 { 186 register int size; 187 register union overhead *op; 188 189 if (cp == NULL) 190 return; 191 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 192 193 /* 194 ** The following botch is because csh tries to free a free block 195 ** when processing the =~ or !~ operators. -- layer@ucbmonet 196 */ 197 #ifdef CSHbotch /* was debug */ 198 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */ 199 #else 200 if (op->ov_magic != MAGIC) 201 return; /* sanity */ 202 #endif 203 204 #ifdef RCHECK 205 ASSERT(op->ov_rmagic == RMAGIC); 206 if (op->ov_index <= 13) 207 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC); 208 #endif 209 ASSERT(op->ov_index < NBUCKETS); 210 size = op->ov_index; 211 op->ov_next = nextf[size]; 212 nextf[size] = op; 213 #ifdef debug 214 nmalloc[size]--; 215 #endif 216 } 217 218 /* 219 * When a program attempts "storage compaction" as mentioned in the 220 * old malloc man page, it realloc's an already freed block. Usually 221 * this is the last block it freed; occasionally it might be farther 222 * back. We have to search all the free lists for the block in order 223 * to determine its bucket: 1st we make one pass thru the lists 224 * checking only the first block in each; if that fails we search 225 * ``realloc_srchlen'' blocks in each list for a match (the variable 226 * is extern so the caller can modify it). If that fails we just copy 227 * however many bytes was given to realloc() and hope it's not huge. 228 */ 229 int realloc_srchlen = 4; /* 4 should be plenty. -1 means whole list */ 230 231 char * 232 realloc(cp, nbytes) 233 char *cp; 234 unsigned nbytes; 235 { 236 register u_int onb; 237 union overhead *op; 238 char *res; 239 register int i; 240 int was_alloced = 0; 241 242 if (cp == NULL) 243 return (malloc(nbytes)); 244 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 245 if (op->ov_magic == MAGIC) { 246 was_alloced++; 247 i = op->ov_index; 248 } 249 else { /* already free: he is doing "compaction" (tee hee) */ 250 if ((i = findbucket(op, 1)) < 0 && 251 (i = findbucket(op, realloc_srchlen)) < 0) 252 i = 0; /* assume smallest possible */ 253 } 254 onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; 255 if (was_alloced && /* avoid the copy if same size block */ 256 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) 257 return(cp); 258 if ((res = malloc(nbytes)) == NULL) 259 return (NULL); 260 if (cp != res) /* common optimization */ 261 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 262 if (was_alloced) 263 free(cp); 264 return (res); 265 } 266 267 /* 268 * Search ``srchlen'' elements of each free list for a block whose 269 * header starts at ``freep''. If srchlen is -1 search the whole list. 270 * Return bucket number, or -1 if not found. 271 */ 272 static 273 findbucket(freep, srchlen) 274 union overhead *freep; 275 int srchlen; 276 { 277 register union overhead *p; 278 register int i, j; 279 280 for (i = 0; i < NBUCKETS; i++) 281 for (j = 0, p = nextf[i]; p && j != srchlen; j++, p = p->ov_next) 282 if (p == freep) 283 return (i); 284 return (-1); 285 } 286 287 #ifdef debug 288 /* 289 * mstats - print out statistics about malloc 290 * 291 * Prints two lines of numbers, one showing the length of the free list 292 * for each size category, the second showing the number of mallocs - 293 * frees for each size category. 294 */ 295 showall(s) 296 char **s; 297 { 298 register int i, j; 299 register union overhead *p; 300 int totfree = 0, 301 totused = 0; 302 303 if (s[1]) 304 printf("Memory allocation statistics %s\nfree:\t", s[1]); 305 for (i = 0; i < NBUCKETS; i++) { 306 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 307 ; 308 309 if (s[1]) 310 printf(" %d", j); 311 totfree += j * (1 << (i + 3)); 312 } 313 if (s[1]) 314 printf("\nused:\t"); 315 for (i = 0; i < NBUCKETS; i++) { 316 if (s[1]) 317 printf(" %d", nmalloc[i]); 318 totused += nmalloc[i] * (1 << (i + 3)); 319 } 320 if (s[1]) 321 printf("\n\t"); 322 printf("Total in use: %d, total free: %d\n", totused, totfree); 323 } 324 #endif 325