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 * If PACK_MALLOC is defined, small blocks are 2^n bytes long.
18 * This is designed for use in a program that uses vast quantities of memory,
19 * but bombs when it runs out.
27 #define DEBUG_m(a) if (debug & 128) a
30 /* I don't much care whether these are defined in sys/types.h--LAW */
32 #define u_char unsigned char
33 #define u_int unsigned int
34 #define u_short unsigned short
36 /* 286 and atarist like big chunks, which gives too much overhead. */
37 #if (defined(RCHECK) || defined(I286) || defined(atarist)) && defined(PACK_MALLOC)
43 * The description below is applicable if PACK_MALLOC is not defined.
45 * The overhead on a block is at least 4 bytes. When free, this space
46 * contains a pointer to the next free block, and the bottom two bits must
47 * be zero. When in use, the first byte is set to MAGIC, and the second
48 * byte is the size index. The remaining bytes are for alignment.
49 * If range checking is enabled and the size of the block fits
50 * in two bytes, then the top two bytes hold the size of the requested block
51 * plus the range checking words, and the header word MINUS ONE.
54 union overhead *ov_next; /* when free */
55 #if MEM_ALIGNBYTES > 4
56 double strut; /* alignment problems */
59 u_char ovu_magic; /* magic number */
60 u_char ovu_index; /* bucket # */
62 u_short ovu_size; /* actual block size */
63 u_int ovu_rmagic; /* range magic number */
66 #define ov_magic ovu.ovu_magic
67 #define ov_index ovu.ovu_index
68 #define ov_size ovu.ovu_size
69 #define ov_rmagic ovu.ovu_rmagic
73 static void botch _((char *s));
75 static void morecore _((int bucket));
76 static int findbucket _((union overhead *freep, int srchlen));
78 #define MAGIC 0xff /* magic # on accounting info */
79 #define RMAGIC 0x55555555 /* magic # on range info */
81 #define RSLOP sizeof (u_int)
88 * In this case it is assumed that if we do sbrk() in 2K units, we
89 * will get 2K aligned blocks. The bucket number of the given subblock is
90 * on the boundary of 2K block which contains the subblock.
91 * Several following bytes contain the magic numbers for the subblocks
94 * Sizes of chunks are powers of 2 for chunks in buckets <=
95 * MAX_PACKED, after this they are (2^n - sizeof(union overhead)) (to
96 * get alignment right).
98 * We suppose that starts of all the chunks in a 2K block are in
99 * different 2^n-byte-long chunks. If the top of the last chunk is
100 * aligned on a boundary of 2K block, this means that
101 * sizeof(union overhead)*"number of chunks" < 2^n, or
102 * sizeof(union overhead)*2K < 4^n, or n > 6 + log2(sizeof()/2)/2, if a
103 * chunk of size 2^n - overhead is used. Since this rules out n = 7
104 * for 8 byte alignment, we specialcase allocation of the first of 16
105 * 128-byte-long chunks.
107 * Note that with the above assumption we automatically have enough
108 * place for MAGIC at the start of 2K block. Note also that we
109 * overlay union overhead over the chunk, thus the start of the chunk
110 * is immediately overwritten after freeing.
112 # define MAX_PACKED 6
113 # define MAX_2_POT_ALGO ((1<<(MAX_PACKED + 1)) - M_OVERHEAD)
114 # define TWOK_MASK ((1<<11) - 1)
115 # define TWOK_MASKED(x) ((u_int)(x) & ~TWOK_MASK)
116 # define TWOK_SHIFT(x) ((u_int)(x) & TWOK_MASK)
117 # define OV_INDEXp(block) ((u_char*)(TWOK_MASKED(block)))
118 # define OV_INDEX(block) (*OV_INDEXp(block))
119 # define OV_MAGIC(block,bucket) (*(OV_INDEXp(block) + \
120 (TWOK_SHIFT(block)>>(bucket + 3)) + \
121 (bucket > MAX_NONSHIFT ? 1 : 0)))
122 # define CHUNK_SHIFT 0
124 static u_char n_blks[11 - 3] = {224, 120, 62, 31, 16, 8, 4, 2};
125 static u_short blk_shift[11 - 3] = {256, 128, 64, 32,
126 16*sizeof(union overhead),
127 8*sizeof(union overhead),
128 4*sizeof(union overhead),
129 2*sizeof(union overhead),
130 # define MAX_NONSHIFT 2 /* Shift 64 greater than chunk 32. */
133 # ifdef DEBUGGING_MSTATS
134 static u_int sbrk_slack;
135 static u_int start_slack;
138 #else /* !PACK_MALLOC */
140 # define OV_MAGIC(block,bucket) (block)->ov_magic
141 # define OV_INDEX(block) (block)->ov_index
142 # define CHUNK_SHIFT 1
143 #endif /* !PACK_MALLOC */
145 # define M_OVERHEAD (sizeof(union overhead) + RSLOP)
148 * Big allocations are often of the size 2^n bytes. To make them a
149 * little bit better, make blocks of size 2^n+pagesize for big n.
152 #ifdef TWO_POT_OPTIMIZE
154 # define PERL_PAGESIZE 4096
155 # define FIRST_BIG_TWO_POT 14 /* 16K */
156 # define FIRST_BIG_BLOCK (1<<FIRST_BIG_TWO_POT) /* 16K */
157 /* If this value or more, check against bigger blocks. */
158 # define FIRST_BIG_BOUND (FIRST_BIG_BLOCK - M_OVERHEAD)
159 /* If less than this value, goes into 2^n-overhead-block. */
160 # define LAST_SMALL_BOUND ((FIRST_BIG_BLOCK>>1) - M_OVERHEAD)
162 #endif /* TWO_POT_OPTIMIZE */
164 #ifdef PERL_EMERGENCY_SBRK
167 # define BIG_SIZE (1<<16) /* 64K */
170 static char *emergency_buffer;
171 static MEM_SIZE emergency_buffer_size;
177 if (size >= BIG_SIZE) {
178 /* Give the possibility to recover: */
179 die("Out of memory during request for %i bytes", size);
180 /* croak may eat too much memory. */
183 if (!emergency_buffer) {
184 /* First offense, give a possibility to recover by dieing. */
185 /* No malloc involved here: */
186 GV **gvp = (GV**)hv_fetch(defstash, "^M", 2, 0);
190 if (!gvp) gvp = (GV**)hv_fetch(defstash, "\015", 1, 0);
191 if (!gvp || !(sv = GvSV(*gvp)) || !SvPOK(sv)
192 || (SvLEN(sv) < (1<<11) - M_OVERHEAD))
193 return (char *)-1; /* Now die die die... */
195 /* Got it, now detach SvPV: */
197 /* Check alignment: */
198 if (((u_int)(pv - M_OVERHEAD)) & ((1<<11) - 1)) {
199 PerlIO_puts(PerlIO_stderr(),"Bad alignment of $^M!\n");
200 return (char *)-1; /* die die die */
203 emergency_buffer = pv - M_OVERHEAD;
204 emergency_buffer_size = SvLEN(sv) + M_OVERHEAD;
207 die("Out of memory!"); /* croak may eat too much memory. */
209 else if (emergency_buffer_size >= size) {
210 emergency_buffer_size -= size;
211 return emergency_buffer + emergency_buffer_size;
214 return (char *)-1; /* poor guy... */
217 #else /* !PERL_EMERGENCY_SBRK */
218 # define emergency_sbrk(size) -1
219 #endif /* !PERL_EMERGENCY_SBRK */
222 * nextf[i] is the pointer to the next free block of size 2^(i+3). The
223 * smallest allocatable block is 8 bytes. The overhead information
224 * precedes the data area returned to the user.
227 static union overhead *nextf[NBUCKETS];
230 #define sbrk(a) Perl_sbrk(a)
231 char * Perl_sbrk _((int size));
236 #ifdef DEBUGGING_MSTATS
238 * nmalloc[i] is the difference between the number of mallocs and frees
239 * for a given block size.
241 static u_int nmalloc[NBUCKETS];
245 #define ASSERT(p) if (!(p)) botch(STRINGIFY(p)); else
250 PerlIO_printf(PerlIO_stderr(), "assertion botched: %s\n", s);
259 register MEM_SIZE nbytes;
261 register union overhead *p;
262 register int bucket = 0;
263 register MEM_SIZE shiftr;
267 MEM_SIZE size = nbytes;
271 if (nbytes > 0xffff) {
272 PerlIO_printf(PerlIO_stderr(), "Allocation too large: %lx\n", (long)nbytes);
275 #endif /* HAS_64K_LIMIT */
277 if ((long)nbytes < 0)
278 croak("panic: malloc");
280 #endif /* PERL_CORE */
283 * Convert amount of memory requested into
284 * closest block size stored in hash buckets
285 * which satisfies request. Account for
286 * space used per block for accounting.
289 if (nbytes > MAX_2_POT_ALGO) {
291 #ifdef TWO_POT_OPTIMIZE
292 if (nbytes >= FIRST_BIG_BOUND) {
293 nbytes -= PERL_PAGESIZE;
296 nbytes += M_OVERHEAD;
297 nbytes = (nbytes + 3) &~ 3;
299 } else if (nbytes == 0) {
303 shiftr = (nbytes - 1) >> 2;
304 /* apart from this loop, this is O(1) */
308 * If nothing in hash bucket right now,
309 * request more memory from the system.
311 if (nextf[bucket] == NULL)
313 if ((p = (union overhead *)nextf[bucket]) == NULL) {
316 PerlIO_puts(PerlIO_stderr(),"Out of memory!\n");
325 DEBUG_m(PerlIO_printf(Perl_debug_log, "0x%lx: (%05d) malloc %ld bytes\n",
326 (unsigned long)(p+1),an++,(long)size));
327 #endif /* PERL_CORE */
329 /* remove from linked list */
331 if (*((int*)p) & (sizeof(union overhead) - 1))
332 PerlIO_printf(PerlIO_stderr(), "Corrupt malloc ptr 0x%lx at 0x%lx\n",
333 (unsigned long)*((int*)p),(unsigned long)p);
335 nextf[bucket] = p->ov_next;
336 OV_MAGIC(p, bucket) = MAGIC;
338 OV_INDEX(p) = bucket;
340 #ifdef DEBUGGING_MSTATS
345 * Record allocated size of block and
346 * bound space with magic numbers.
348 if (nbytes <= 0x10000)
349 p->ov_size = nbytes - 1;
350 p->ov_rmagic = RMAGIC;
351 *((u_int *)((caddr_t)p + nbytes - RSLOP)) = RMAGIC;
353 return ((Malloc_t)(p + CHUNK_SHIFT));
357 * Allocate more memory to the indicated bucket.
363 register union overhead *op;
364 register int rnu; /* 2^rnu bytes will be requested */
365 register int nblks; /* become nblks blocks of the desired size */
366 register MEM_SIZE siz, needed;
371 if (bucket == (sizeof(MEM_SIZE)*8 - 3)) {
372 croak("Allocation too large");
375 * Insure memory is allocated
376 * on a page boundary. Should
377 * make getpageize call?
379 #ifndef atarist /* on the atari we dont have to worry about this */
380 op = (union overhead *)sbrk(0);
383 if ((u_int)op & 0x7ff)
384 (void)sbrk(slack = 2048 - ((u_int)op & 0x7ff));
386 if ((u_int)op & 0x3ff)
387 (void)sbrk(slack = 1024 - ((u_int)op & 0x3ff));
389 # if defined(DEBUGGING_MSTATS) && defined(PACK_MALLOC)
393 /* The sbrk(0) call on the I286 always returns the next segment */
397 #if !(defined(I286) || defined(atarist))
398 /* take 2k unless the block is bigger than that */
399 rnu = (bucket <= 8) ? 11 : bucket + 3;
401 /* take 16k unless the block is bigger than that
402 (80286s like large segments!), probably good on the atari too */
403 rnu = (bucket <= 11) ? 14 : bucket + 3;
405 nblks = 1 << (rnu - (bucket + 3)); /* how many blocks to get */
406 needed = (MEM_SIZE)1 << rnu;
407 #ifdef TWO_POT_OPTIMIZE
408 needed += (bucket >= (FIRST_BIG_TWO_POT - 3) ? PERL_PAGESIZE : 0);
410 op = (union overhead *)sbrk(needed);
412 if (op == (union overhead *)-1) {
413 op = (union overhead *)emergency_sbrk(needed);
414 if (op == (union overhead *)-1)
418 * Round up to minimum allocation size boundary
419 * and deduct from block count to reflect.
423 if ((u_int)op & 0x7ff)
424 croak("panic: Off-page sbrk");
427 op = (union overhead *)(((MEM_SIZE)op + 8) &~ 7);
431 /* Again, this should always be ok on an 80286 */
434 * Add new memory allocated to that on
435 * free list for this hash bucket.
437 siz = 1 << (bucket + 3);
439 *(u_char*)op = bucket; /* Fill index. */
440 if (bucket <= MAX_PACKED - 3) {
441 op = (union overhead *) ((char*)op + blk_shift[bucket]);
442 nblks = n_blks[bucket];
443 # ifdef DEBUGGING_MSTATS
444 start_slack += blk_shift[bucket];
446 } else if (bucket <= 11 - 1 - 3) {
447 op = (union overhead *) ((char*)op + blk_shift[bucket]);
448 /* nblks = n_blks[bucket]; */
449 siz -= sizeof(union overhead);
450 } else op++; /* One chunk per block. */
451 #endif /* !PACK_MALLOC */
453 while (--nblks > 0) {
454 op->ov_next = (union overhead *)((caddr_t)op + siz);
455 op = (union overhead *)((caddr_t)op + siz);
457 /* Not all sbrks return zeroed memory.*/
458 op->ov_next = (union overhead *)NULL;
460 if (bucket == 7 - 3) { /* Special case, explanation is above. */
461 union overhead *n_op = nextf[7 - 3]->ov_next;
462 nextf[7 - 3] = (union overhead *)((caddr_t)nextf[7 - 3]
463 - sizeof(union overhead));
464 nextf[7 - 3]->ov_next = n_op;
466 #endif /* !PACK_MALLOC */
473 register MEM_SIZE size;
474 register union overhead *op;
475 char *cp = (char*)mp;
481 DEBUG_m(PerlIO_printf(Perl_debug_log, "0x%lx: (%05d) free\n",(unsigned long)cp,an++));
482 #endif /* PERL_CORE */
486 op = (union overhead *)((caddr_t)cp
487 - sizeof (union overhead) * CHUNK_SHIFT);
489 bucket = OV_INDEX(op);
492 ASSERT(OV_MAGIC(op, bucket) == MAGIC); /* make sure it was in use */
494 if (OV_MAGIC(op, bucket) != MAGIC) {
495 static bad_free_warn = -1;
496 if (bad_free_warn == -1) {
497 char *pbf = getenv("PERL_BADFREE");
498 bad_free_warn = (pbf) ? atoi(pbf) : 1;
503 warn("%s free() ignored",
504 op->ov_rmagic == RMAGIC - 1 ? "Duplicate" : "Bad");
506 warn("Bad free() ignored");
512 ASSERT(op->ov_rmagic == RMAGIC);
513 if (OV_INDEX(op) <= 13)
514 ASSERT(*(u_int *)((caddr_t)op + op->ov_size + 1 - RSLOP) == RMAGIC);
515 op->ov_rmagic = RMAGIC - 1;
517 ASSERT(OV_INDEX(op) < NBUCKETS);
519 op->ov_next = nextf[size];
521 #ifdef DEBUGGING_MSTATS
527 * When a program attempts "storage compaction" as mentioned in the
528 * old malloc man page, it realloc's an already freed block. Usually
529 * this is the last block it freed; occasionally it might be farther
530 * back. We have to search all the free lists for the block in order
531 * to determine its bucket: 1st we make one pass thru the lists
532 * checking only the first block in each; if that fails we search
533 * ``reall_srchlen'' blocks in each list for a match (the variable
534 * is extern so the caller can modify it). If that fails we just copy
535 * however many bytes was given to realloc() and hope it's not huge.
537 int reall_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */
544 register MEM_SIZE onb;
549 char *cp = (char*)mp;
553 MEM_SIZE size = nbytes;
557 if (nbytes > 0xffff) {
558 PerlIO_printf(PerlIO_stderr(), "Reallocation too large: %lx\n", size);
561 #endif /* HAS_64K_LIMIT */
563 return malloc(nbytes);
565 if ((long)nbytes < 0)
566 croak("panic: realloc");
568 #endif /* PERL_CORE */
570 op = (union overhead *)((caddr_t)cp
571 - sizeof (union overhead) * CHUNK_SHIFT);
573 if (OV_MAGIC(op, i) == MAGIC) {
577 * Already free, doing "compaction".
579 * Search for the old block of memory on the
580 * free list. First, check the most common
581 * case (last element free'd), then (this failing)
582 * the last ``reall_srchlen'' items free'd.
583 * If all lookups fail, then assume the size of
584 * the memory block being realloc'd is the
587 if ((i = findbucket(op, 1)) < 0 &&
588 (i = findbucket(op, reall_srchlen)) < 0)
591 onb = (1L << (i + 3)) -
593 (i <= (MAX_PACKED - 3) ? 0 : M_OVERHEAD)
597 #ifdef TWO_POT_OPTIMIZE
598 + (i >= (FIRST_BIG_TWO_POT - 3) ? PERL_PAGESIZE : 0)
602 * avoid the copy if same size block.
603 * We are not agressive with boundary cases. Note that it is
604 * possible for small number of cases give false negative if
605 * both new size and old one are in the bucket for
606 * FIRST_BIG_TWO_POT, but the new one is near the lower end.
609 nbytes <= onb && (nbytes > ( (onb >> 1) - M_OVERHEAD )
610 #ifdef TWO_POT_OPTIMIZE
611 || (i == (FIRST_BIG_TWO_POT - 3)
612 && nbytes >= LAST_SMALL_BOUND )
617 * Record new allocated size of block and
618 * bound space with magic numbers.
620 if (OV_INDEX(op) <= 13) {
622 * Convert amount of memory requested into
623 * closest block size stored in hash buckets
624 * which satisfies request. Account for
625 * space used per block for accounting.
627 nbytes += M_OVERHEAD;
628 nbytes = (nbytes + 3) &~ 3;
629 op->ov_size = nbytes - 1;
630 *((u_int *)((caddr_t)op + nbytes - RSLOP)) = RMAGIC;
636 if ((res = (char*)malloc(nbytes)) == NULL)
638 if (cp != res) /* common optimization */
639 Copy(cp, res, (MEM_SIZE)(nbytes<onb?nbytes:onb), char);
647 PerlIO_printf(PerlIO_stderr(), "0x%lx: (%05d) rfree\n",(unsigned long)res,an++);
648 PerlIO_printf(PerlIO_stderr(), "0x%lx: (%05d) realloc %ld bytes\n",
649 (unsigned long)res,an++,(long)size);
652 #endif /* PERL_CORE */
653 return ((Malloc_t)res);
657 * Search ``srchlen'' elements of each free list for a block whose
658 * header starts at ``freep''. If srchlen is -1 search the whole list.
659 * Return bucket number, or -1 if not found.
662 findbucket(freep, srchlen)
663 union overhead *freep;
666 register union overhead *p;
669 for (i = 0; i < NBUCKETS; i++) {
671 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) {
681 calloc(elements, size)
682 register MEM_SIZE elements;
683 register MEM_SIZE size;
685 long sz = elements * size;
686 Malloc_t p = malloc(sz);
689 memset((void*)p, 0, sz);
694 #ifdef DEBUGGING_MSTATS
696 * mstats - print out statistics about malloc
698 * Prints two lines of numbers, one showing the length of the free list
699 * for each size category, the second showing the number of mallocs -
700 * frees for each size category.
707 register union overhead *p;
708 int topbucket=0, totfree=0, totused=0;
709 u_int nfree[NBUCKETS];
711 for (i=0; i < NBUCKETS; i++) {
712 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
715 totfree += nfree[i] * (1 << (i + 3));
716 totused += nmalloc[i] * (1 << (i + 3));
717 if (nfree[i] || nmalloc[i])
721 PerlIO_printf(PerlIO_stderr(), "Memory allocation statistics %s (buckets 8..%d)\n",
722 s, (1 << (topbucket + 3)) );
723 PerlIO_printf(PerlIO_stderr(), " %7d free: ", totfree);
724 for (i=0; i <= topbucket; i++) {
725 PerlIO_printf(PerlIO_stderr(), (i<5)?" %5d":" %3d", nfree[i]);
727 PerlIO_printf(PerlIO_stderr(), "\n %7d used: ", totused);
728 for (i=0; i <= topbucket; i++) {
729 PerlIO_printf(PerlIO_stderr(), (i<5)?" %5d":" %3d", nmalloc[i]);
731 PerlIO_printf(PerlIO_stderr(), "\n");
733 if (sbrk_slack || start_slack) {
734 PerlIO_printf(PerlIO_stderr(), "Odd ends: %7d bytes from sbrk(), %7d from malloc.\n",
735 sbrk_slack, start_slack);
752 # define PERL_SBRK_VIA_MALLOC
755 # ifdef PERL_SBRK_VIA_MALLOC
759 # include "Error: -DPERL_SBRK_VIA_MALLOC requires -DHIDEMYMALLOC"
762 /* it may seem schizophrenic to use perl's malloc and let it call system */
763 /* malloc, the reason for that is only the 3.2 version of the OS that had */
764 /* frequent core dumps within nxzonefreenolock. This sbrk routine put an */
765 /* end to the cores */
767 # define SYSTEM_ALLOC(a) malloc(a)
769 # endif /* PERL_SBRK_VIA_MALLOC */
771 static IV Perl_sbrk_oldchunk;
772 static long Perl_sbrk_oldsize;
774 # define PERLSBRK_32_K (1<<15)
775 # define PERLSBRK_64_K (1<<16)
786 reqsize = size; /* just for the DEBUG_m statement */
788 if (size <= Perl_sbrk_oldsize) {
789 got = Perl_sbrk_oldchunk;
790 Perl_sbrk_oldchunk += size;
791 Perl_sbrk_oldsize -= size;
793 if (size >= PERLSBRK_32_K) {
799 size = PERLSBRK_64_K;
802 got = (IV)SYSTEM_ALLOC(size);
804 /* Chunk is small, register the rest for future allocs. */
805 Perl_sbrk_oldchunk = got + reqsize;
806 Perl_sbrk_oldsize = size - reqsize;
811 DEBUG_m(PerlIO_printf(PerlIO_stderr(), "sbrk malloc size %ld (reqsize %ld), left size %ld, give addr 0x%lx\n",
812 size, reqsize, Perl_sbrk_oldsize, got));
818 #endif /* ! defined USE_PERL_SBRK */