1 #ifndef lint 2 static char *sccsid = "@(#)alloc.c 4.4 (Berkeley from Caltech) 12/13/84"; 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 /* 64 * nmalloc[i] is the difference between the number of mallocs and frees 65 * for a given block size. 66 */ 67 static u_int nmalloc[NBUCKETS]; 68 69 #ifdef debug 70 #define ASSERT(p) if (!(p)) botch("p"); else 71 static 72 botch(s) 73 char *s; 74 { 75 printf("assertion botched: %s\n",s); 76 abort(); 77 } 78 #else 79 #define ASSERT(p) 80 #endif 81 82 char * 83 malloc(nbytes) 84 register unsigned nbytes; 85 { 86 register union overhead *p; 87 register int bucket = 0; 88 register unsigned shiftr; 89 90 /* 91 * Convert amount of memory requested into 92 * closest block size stored in hash buckets 93 * which satisfies request. Account for 94 * space used per block for accounting. 95 */ 96 nbytes += sizeof (union overhead) + RSLOP; 97 nbytes = (nbytes + 3) &~ 3; 98 shiftr = (nbytes - 1) >> 2; 99 /* apart from this loop, this is O(1) */ 100 while (shiftr >>= 1) 101 bucket++; 102 /* 103 * If nothing in hash bucket right now, 104 * request more memory from the system. 105 */ 106 if (nextf[bucket] == NULL) 107 morecore(bucket); 108 if ((p = (union overhead *)nextf[bucket]) == NULL) 109 return (NULL); 110 /* remove from linked list */ 111 nextf[bucket] = nextf[bucket]->ov_next; 112 p->ov_magic = MAGIC; 113 p->ov_index= bucket; 114 nmalloc[bucket]++; 115 #ifdef RCHECK 116 /* 117 * Record allocated size of block and 118 * bound space with magic numbers. 119 */ 120 if (nbytes <= 0x10000) 121 p->ov_size = nbytes - 1; 122 p->ov_rmagic = RMAGIC; 123 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC; 124 #endif 125 return ((char *)(p + 1)); 126 } 127 128 /* 129 * Allocate more memory to the indicated bucket. 130 */ 131 static 132 morecore(bucket) 133 register bucket; 134 { 135 register union overhead *op; 136 register int rnu; /* 2^rnu bytes will be requested */ 137 register int nblks; /* become nblks blocks of the desired size */ 138 register int siz; 139 140 if (nextf[bucket]) 141 return; 142 /* 143 * Insure memory is allocated 144 * on a page boundary. Should 145 * make getpageize call? 146 */ 147 op = (union overhead *)sbrk(0); 148 if ((int)op & 0x3ff) 149 (void) sbrk(1024 - ((int)op & 0x3ff)); 150 /* take 2k unless the block is bigger than that */ 151 rnu = (bucket <= 8) ? 11 : bucket + 3; 152 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */ 153 if (rnu < bucket) 154 rnu = bucket; 155 op = (union overhead *)sbrk(1 << rnu); 156 /* no more room! */ 157 if ((int)op == -1) 158 return; 159 /* 160 * Round up to minimum allocation size boundary 161 * and deduct from block count to reflect. 162 */ 163 if ((int)op & 7) { 164 op = (union overhead *)(((int)op + 8) &~ 7); 165 nblks--; 166 } 167 /* 168 * Add new memory allocated to that on 169 * free list for this hash bucket. 170 */ 171 nextf[bucket] = op; 172 siz = 1 << (bucket + 3); 173 while (--nblks > 0) { 174 op->ov_next = (union overhead *)((caddr_t)op + siz); 175 op = (union overhead *)((caddr_t)op + siz); 176 } 177 } 178 179 free(cp) 180 char *cp; 181 { 182 register int size; 183 register union overhead *op; 184 185 if (cp == NULL) 186 return; 187 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 188 189 /* 190 ** The following botch is because csh tries to free a free block 191 ** when processing the =~ or !~ operators. -- layer@ucbmonet 192 */ 193 #ifdef CSHbotch /* was 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 199 200 #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 nmalloc[size]--; 210 } 211 212 /* 213 * When a program attempts "storage compaction" as mentioned in the 214 * old malloc man page, it realloc's an already freed block. Usually 215 * this is the last block it freed; occasionally it might be farther 216 * back. We have to search all the free lists for the block in order 217 * to determine its bucket: 1st we make one pass thru the lists 218 * checking only the first block in each; if that fails we search 219 * ``realloc_srchlen'' blocks in each list for a match (the variable 220 * is extern so the caller can modify it). If that fails we just copy 221 * however many bytes was given to realloc() and hope it's not huge. 222 */ 223 int realloc_srchlen = 4; /* 4 should be plenty. -1 means whole list */ 224 225 char * 226 realloc(cp, nbytes) 227 char *cp; 228 unsigned nbytes; 229 { 230 register u_int onb; 231 union overhead *op; 232 char *res; 233 register int i; 234 int was_alloced = 0; 235 236 if (cp == NULL) 237 return (malloc(nbytes)); 238 op = (union overhead *)((caddr_t)cp - sizeof (union overhead)); 239 if (op->ov_magic == MAGIC) { 240 was_alloced++; 241 i = op->ov_index; 242 } 243 else { /* already free: he is doing "compaction" (tee hee) */ 244 if ((i = findbucket(op, 1)) < 0 && 245 (i = findbucket(op, realloc_srchlen)) < 0) 246 i = 0; /* assume smallest possible */ 247 } 248 onb = (1 << (i + 3)) - sizeof (*op) - RSLOP; 249 if (was_alloced && /* avoid the copy if same size block */ 250 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) 251 return(cp); 252 if ((res = malloc(nbytes)) == NULL) 253 return (NULL); 254 if (cp != res) /* common optimization */ 255 bcopy(cp, res, (nbytes < onb) ? nbytes : onb); 256 if (was_alloced) 257 free(cp); 258 return (res); 259 } 260 261 /* 262 * Search ``srchlen'' elements of each free list for a block whose 263 * header starts at ``freep''. If srchlen is -1 search the whole list. 264 * Return bucket number, or -1 if not found. 265 */ 266 static 267 findbucket(freep, srchlen) 268 union overhead *freep; 269 int srchlen; 270 { 271 register union overhead *p; 272 register int i, j; 273 274 for (i = 0; i < NBUCKETS; i++) 275 for (j = 0, p = nextf[i]; p && j != srchlen; j++, p = p->ov_next) 276 if (p == freep) 277 return (i); 278 return (-1); 279 } 280 281 /* 282 * mstats - print out statistics about malloc 283 * 284 * Prints two lines of numbers, one showing the length of the free list 285 * for each size category, the second showing the number of mallocs - 286 * frees for each size category. 287 */ 288 showall(s) 289 char **s; 290 { 291 register int i, j; 292 register union overhead *p; 293 int totfree = 0, 294 totused = 0; 295 296 if (s[1]) 297 printf("Memory allocation statistics %s\nfree:", s[1]); 298 for (i = 0; i < NBUCKETS; i++) { 299 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++) 300 ; 301 302 if (s[1]) 303 printf(" %d", j); 304 totfree += j * (1 << (i + 3)); 305 } 306 if (s[1]) 307 printf("\nused:"); 308 for (i = 0; i < NBUCKETS; i++) { 309 if (s[1]) 310 printf(" %d", nmalloc[i]); 311 totused += nmalloc[i] * (1 << (i + 3)); 312 } 313 if (s[1]) 314 printf("\n"); 315 printf("Total in use: %d, total free: %d\n", totused, totfree); 316 } 317