10 * malloc.c (Caltech) 2/21/82
11 * Chris Kingsley, kingsley@cit-20.
13 * This is a very fast storage allocator. It allocates blocks of a small
14 * number of different sizes, and keeps free lists of each size. Blocks that
15 * don't exactly fit are passed up to the next larger size. In this
16 * implementation, the available sizes are 2^n-4 (or 2^n-12) bytes long.
17 * This is designed for use in a program that uses vast quantities of memory,
18 * but bombs when it runs out.
24 /* I don't much care whether these are defined in sys/types.h--LAW */
26 #define u_char unsigned char
27 #define u_int unsigned int
28 #define u_short unsigned short
31 * The overhead on a block is at least 4 bytes. When free, this space
32 * contains a pointer to the next free block, and the bottom two bits must
33 * be zero. When in use, the first byte is set to MAGIC, and the second
34 * byte is the size index. The remaining bytes are for alignment.
35 * If range checking is enabled and the size of the block fits
36 * in two bytes, then the top two bytes hold the size of the requested block
37 * plus the range checking words, and the header word MINUS ONE.
40 union overhead *ov_next; /* when free */
41 #if MEM_ALIGNBYTES > 4
42 double strut; /* alignment problems */
45 u_char ovu_magic; /* magic number */
46 u_char ovu_index; /* bucket # */
48 u_short ovu_size; /* actual block size */
49 u_int ovu_rmagic; /* range magic number */
52 #define ov_magic ovu.ovu_magic
53 #define ov_index ovu.ovu_index
54 #define ov_size ovu.ovu_size
55 #define ov_rmagic ovu.ovu_rmagic
59 static void botch _((char *s));
61 static void morecore _((int bucket));
62 static int findbucket _((union overhead *freep, int srchlen));
64 #define MAGIC 0xff /* magic # on accounting info */
65 #define RMAGIC 0x55555555 /* magic # on range info */
67 #define RSLOP sizeof (u_int)
73 * nextf[i] is the pointer to the next free block of size 2^(i+3). The
74 * smallest allocatable block is 8 bytes. The overhead information
75 * precedes the data area returned to the user.
78 static union overhead *nextf[NBUCKETS];
81 #ifdef DEBUGGING_MSTATS
83 * nmalloc[i] is the difference between the number of mallocs and frees
84 * for a given block size.
86 static u_int nmalloc[NBUCKETS];
91 #define ASSERT(p) if (!(p)) botch("p"); else
97 printf("assertion botched: %s\n", s);
106 register MEM_SIZE nbytes;
108 register union overhead *p;
109 register int bucket = 0;
110 register MEM_SIZE shiftr;
114 MEM_SIZE size = nbytes;
118 if (nbytes > 0xffff) {
119 fprintf(stderr, "Allocation too large: %lx\n", (long)nbytes);
124 if ((long)nbytes < 0)
125 croak("panic: malloc");
127 #endif /* safemalloc */
129 MUTEX_LOCK(&malloc_mutex);
131 * Convert amount of memory requested into
132 * closest block size stored in hash buckets
133 * which satisfies request. Account for
134 * space used per block for accounting.
136 nbytes += sizeof (union overhead) + RSLOP;
137 nbytes = (nbytes + 3) &~ 3;
138 shiftr = (nbytes - 1) >> 2;
139 /* apart from this loop, this is O(1) */
143 * If nothing in hash bucket right now,
144 * request more memory from the system.
146 if (nextf[bucket] == NULL)
148 if ((p = (union overhead *)nextf[bucket]) == NULL) {
149 MUTEX_UNLOCK(&malloc_mutex);
152 fputs("Out of memory!\n", stderr);
161 DEBUG_m(fprintf(stderr,"0x%lx: (%05d) malloc %ld bytes\n",
162 (unsigned long)(p+1),an++,(long)size));
163 #endif /* safemalloc */
165 /* remove from linked list */
167 if (*((int*)p) & (sizeof(union overhead) - 1))
168 fprintf(stderr,"Corrupt malloc ptr 0x%lx at 0x%lx\n",
169 (unsigned long)*((int*)p),(unsigned long)p);
171 nextf[bucket] = p->ov_next;
174 #ifdef DEBUGGING_MSTATS
179 * Record allocated size of block and
180 * bound space with magic numbers.
182 if (nbytes <= 0x10000)
183 p->ov_size = nbytes - 1;
184 p->ov_rmagic = RMAGIC;
185 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC;
187 MUTEX_UNLOCK(&malloc_mutex);
188 return ((Malloc_t)(p + 1));
192 * Allocate more memory to the indicated bucket.
198 register union overhead *op;
199 register int rnu; /* 2^rnu bytes will be requested */
200 register int nblks; /* become nblks blocks of the desired size */
201 register MEM_SIZE siz;
206 * Insure memory is allocated
207 * on a page boundary. Should
208 * make getpageize call?
210 #ifndef atarist /* on the atari we dont have to worry about this */
211 op = (union overhead *)sbrk(0);
214 (void)sbrk(1024 - ((int)op & 0x3ff));
216 /* The sbrk(0) call on the I286 always returns the next segment */
220 #if !(defined(I286) || defined(atarist))
221 /* take 2k unless the block is bigger than that */
222 rnu = (bucket <= 8) ? 11 : bucket + 3;
224 /* take 16k unless the block is bigger than that
225 (80286s like large segments!), probably good on the atari too */
226 rnu = (bucket <= 11) ? 14 : bucket + 3;
228 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */
231 op = (union overhead *)sbrk(1L << rnu);
236 * Round up to minimum allocation size boundary
237 * and deduct from block count to reflect.
241 op = (union overhead *)(((MEM_SIZE)op + 8) &~ 7);
245 /* Again, this should always be ok on an 80286 */
248 * Add new memory allocated to that on
249 * free list for this hash bucket.
252 siz = 1 << (bucket + 3);
253 while (--nblks > 0) {
254 op->ov_next = (union overhead *)((caddr_t)op + siz);
255 op = (union overhead *)((caddr_t)op + siz);
263 register MEM_SIZE size;
264 register union overhead *op;
265 char *cp = (char*)mp;
268 DEBUG_m(fprintf(stderr,"0x%lx: (%05d) free\n",(unsigned long)cp,an++));
269 #endif /* safemalloc */
273 op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
275 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */
277 if (op->ov_magic != MAGIC) {
279 warn("%s free() ignored",
280 op->ov_rmagic == RMAGIC - 1 ? "Duplicate" : "Bad");
282 warn("Bad free() ignored");
287 MUTEX_LOCK(&malloc_mutex);
289 ASSERT(op->ov_rmagic == RMAGIC);
290 if (op->ov_index <= 13)
291 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC);
292 op->ov_rmagic = RMAGIC - 1;
294 ASSERT(op->ov_index < NBUCKETS);
296 op->ov_next = nextf[size];
298 #ifdef DEBUGGING_MSTATS
301 MUTEX_UNLOCK(&malloc_mutex);
305 * When a program attempts "storage compaction" as mentioned in the
306 * old malloc man page, it realloc's an already freed block. Usually
307 * this is the last block it freed; occasionally it might be farther
308 * back. We have to search all the free lists for the block in order
309 * to determine its bucket: 1st we make one pass thru the lists
310 * checking only the first block in each; if that fails we search
311 * ``reall_srchlen'' blocks in each list for a match (the variable
312 * is extern so the caller can modify it). If that fails we just copy
313 * however many bytes was given to realloc() and hope it's not huge.
315 int reall_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */
322 register MEM_SIZE onb;
327 char *cp = (char*)mp;
331 MEM_SIZE size = nbytes;
335 if (nbytes > 0xffff) {
336 fprintf(stderr, "Reallocation too large: %lx\n", size);
341 return malloc(nbytes);
343 if ((long)nbytes < 0)
344 croak("panic: realloc");
346 #endif /* safemalloc */
348 MUTEX_LOCK(&malloc_mutex);
349 op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
350 if (op->ov_magic == MAGIC) {
355 * Already free, doing "compaction".
357 * Search for the old block of memory on the
358 * free list. First, check the most common
359 * case (last element free'd), then (this failing)
360 * the last ``reall_srchlen'' items free'd.
361 * If all lookups fail, then assume the size of
362 * the memory block being realloc'd is the
365 if ((i = findbucket(op, 1)) < 0 &&
366 (i = findbucket(op, reall_srchlen)) < 0)
369 onb = (1L << (i + 3)) - sizeof (*op) - RSLOP;
370 /* avoid the copy if same size block */
372 nbytes <= onb && nbytes > (onb >> 1) - sizeof(*op) - RSLOP) {
375 * Record new allocated size of block and
376 * bound space with magic numbers.
378 if (op->ov_index <= 13) {
380 * Convert amount of memory requested into
381 * closest block size stored in hash buckets
382 * which satisfies request. Account for
383 * space used per block for accounting.
385 nbytes += sizeof (union overhead) + RSLOP;
386 nbytes = (nbytes + 3) &~ 3;
387 op->ov_size = nbytes - 1;
388 *((u_int *)((caddr_t)op + nbytes - RSLOP)) = RMAGIC;
392 MUTEX_UNLOCK(&malloc_mutex);
395 MUTEX_UNLOCK(&malloc_mutex);
396 if ((res = (char*)malloc(nbytes)) == NULL)
398 if (cp != res) /* common optimization */
399 Copy(cp, res, (MEM_SIZE)(nbytes<onb?nbytes:onb), char);
407 fprintf(stderr,"0x%lx: (%05d) rfree\n",(unsigned long)res,an++);
408 fprintf(stderr,"0x%lx: (%05d) realloc %ld bytes\n",
409 (unsigned long)res,an++,(long)size);
412 #endif /* safemalloc */
413 return ((Malloc_t)res);
417 * Search ``srchlen'' elements of each free list for a block whose
418 * header starts at ``freep''. If srchlen is -1 search the whole list.
419 * Return bucket number, or -1 if not found.
422 findbucket(freep, srchlen)
423 union overhead *freep;
426 register union overhead *p;
429 for (i = 0; i < NBUCKETS; i++) {
431 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) {
440 #ifdef DEBUGGING_MSTATS
442 * mstats - print out statistics about malloc
444 * Prints two lines of numbers, one showing the length of the free list
445 * for each size category, the second showing the number of mallocs -
446 * frees for each size category.
453 register union overhead *p;
454 int topbucket=0, totfree=0, totused=0;
455 u_int nfree[NBUCKETS];
457 for (i=0; i < NBUCKETS; i++) {
458 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
461 totfree += nfree[i] * (1 << (i + 3));
462 totused += nmalloc[i] * (1 << (i + 3));
463 if (nfree[i] || nmalloc[i])
467 fprintf(stderr, "Memory allocation statistics %s (buckets 8..%d)\n",
468 s, (1 << (topbucket + 3)) );
469 fprintf(stderr, " %7d free: ", totfree);
470 for (i=0; i <= topbucket; i++) {
471 fprintf(stderr, (i<5)?" %5d":" %3d", nfree[i]);
473 fprintf(stderr, "\n %7d used: ", totused);
474 for (i=0; i <= topbucket; i++) {
475 fprintf(stderr, (i<5)?" %5d":" %3d", nmalloc[i]);
477 fprintf(stderr, "\n");