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35 * malloc.c (Caltech) 2/21/82
36 * Chris Kingsley, kingsley@cit-20.
38 * This is a very fast storage allocator. It allocates blocks of a small
39 * number of different sizes, and keeps free lists of each size. Blocks that
40 * don't exactly fit are passed up to the next larger size. In this
41 * implementation, the available sizes are 2^n-4 (or 2^n-10) bytes long.
42 * This is designed for use in a virtual memory environment.
45 #include <sys/types.h>
52 #include <sys/param.h>
54 #include "rtld_printf.h"
56 #define MAP_COPY MAP_PRIVATE
61 #ifndef BSD /* Need do better than this */
62 #define NEED_DEV_ZERO 1
65 static void morecore();
66 static int findbucket();
69 * Pre-allocate mmap'ed pages
71 #define NPOOLPAGES (32*1024/pagesz)
72 static caddr_t pagepool_start, pagepool_end;
73 static int morepages();
76 * The overhead on a block is at least 4 bytes. When free, this space
77 * contains a pointer to the next free block, and the bottom two bits must
78 * be zero. When in use, the first byte is set to MAGIC, and the second
79 * byte is the size index. The remaining bytes are for alignment.
80 * If range checking is enabled then a second word holds the size of the
81 * requested block, less 1, rounded up to a multiple of sizeof(RMAGIC).
82 * The order of elements is critical: ov_magic must overlay the low order
83 * bits of ov_next, and ov_magic can not be a valid ov_next bit pattern.
86 union overhead *ov_next; /* when free */
88 u_char ovu_magic; /* magic number */
89 u_char ovu_index; /* bucket # */
91 u_short ovu_rmagic; /* range magic number */
92 u_int ovu_size; /* actual block size */
95 #define ov_magic ovu.ovu_magic
96 #define ov_index ovu.ovu_index
97 #define ov_rmagic ovu.ovu_rmagic
98 #define ov_size ovu.ovu_size
101 #define MAGIC 0xef /* magic # on accounting info */
102 #define RMAGIC 0x5555 /* magic # on range info */
105 #define RSLOP sizeof (u_short)
111 * nextf[i] is the pointer to the next free block of size 2^(i+3). The
112 * smallest allocatable block is 8 bytes. The overhead information
113 * precedes the data area returned to the user.
116 static union overhead *nextf[NBUCKETS];
118 static int pagesz; /* page size */
119 static int pagebucket; /* page size bucket */
123 * nmalloc[i] is the difference between the number of mallocs and frees
124 * for a given block size.
126 static u_int nmalloc[NBUCKETS];
130 #if defined(MALLOC_DEBUG) || defined(RCHECK)
131 #define ASSERT(p) if (!(p)) botch("p")
137 fprintf(stderr, "\r\nassertion botched: %s\r\n", s);
138 (void) fflush(stderr); /* just in case user buffered it */
145 /* Debugging stuff */
146 #define TRACE() rtld_printf("TRACE %s:%d\n", __FILE__, __LINE__)
152 register union overhead *op;
155 register unsigned amt;
158 * First time malloc is called, setup page size and
159 * align break pointer so all data will be page aligned.
162 pagesz = n = getpagesize();
163 if (morepages(NPOOLPAGES) == 0)
165 op = (union overhead *)(pagepool_start);
166 n = n - sizeof (*op) - ((long)op & (n - 1));
174 while ((unsigned)pagesz > amt) {
181 * Convert amount of memory requested into closest block size
182 * stored in hash buckets which satisfies request.
183 * Account for space used per block for accounting.
185 if (nbytes <= (unsigned long)(n = pagesz - sizeof (*op) - RSLOP)) {
187 amt = 8; /* size of first bucket */
190 amt = 16; /* size of first bucket */
193 n = -(sizeof (*op) + RSLOP);
198 while (nbytes > amt + n) {
205 * If nothing in hash bucket right now,
206 * request more memory from the system.
208 if ((op = nextf[bucket]) == NULL) {
210 if ((op = nextf[bucket]) == NULL)
213 /* remove from linked list */
214 nextf[bucket] = op->ov_next;
215 op->ov_magic = MAGIC;
216 op->ov_index = bucket;
222 * Record allocated size of block and
223 * bound space with magic numbers.
225 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
226 op->ov_rmagic = RMAGIC;
227 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
229 return ((char *)(op + 1));
233 * Used by rtld.c, if we don't override it here the calloc from
234 * libc may try to pull in the malloc/realloc/free from libc too.
237 calloc(size_t num, size_t size)
242 if ((p = malloc(size)) != NULL)
248 * Allocate more memory to the indicated bucket.
254 register union overhead *op;
255 register int sz; /* size of desired block */
256 int amt; /* amount to allocate */
257 int nblks; /* how many blocks we get */
260 * sbrk_size <= 0 only for big, FLUFFY, requests (about
261 * 2^30 bytes on a VAX, I think) or for a negative arg.
263 sz = 1 << (bucket + 3);
277 if (amt > pagepool_end - pagepool_start)
278 if (morepages(amt/pagesz + NPOOLPAGES) == 0)
280 op = (union overhead *)pagepool_start;
281 pagepool_start += amt;
284 * Add new memory allocated to that on
285 * free list for this hash bucket.
288 while (--nblks > 0) {
289 op->ov_next = (union overhead *)((caddr_t)op + sz);
290 op = (union overhead *)((caddr_t)op + sz);
299 register union overhead *op;
303 op = (union overhead *)((caddr_t)cp - sizeof (union overhead));
305 ASSERT(op->ov_magic == MAGIC); /* make sure it was in use */
307 if (op->ov_magic != MAGIC)
311 ASSERT(op->ov_rmagic == RMAGIC);
312 ASSERT(*(u_short *)((caddr_t)(op + 1) + op->ov_size) == RMAGIC);
315 ASSERT(size < NBUCKETS);
316 op->ov_next = nextf[size]; /* also clobbers ov_magic */
324 * When a program attempts "storage compaction" as mentioned in the
325 * old malloc man page, it realloc's an already freed block. Usually
326 * this is the last block it freed; occasionally it might be farther
327 * back. We have to search all the free lists for the block in order
328 * to determine its bucket: 1st we make one pass thru the lists
329 * checking only the first block in each; if that fails we search
330 * ``realloc_srchlen'' blocks in each list for a match (the variable
331 * is extern so the caller can modify it). If that fails we just copy
332 * however many bytes was given to realloc() and hope it's not huge.
334 int realloc_srchlen = 4; /* 4 should be plenty, -1 =>'s whole list */
348 return (malloc(nbytes));
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 ``realloc_srchlen'' items free'd.
361 * If all lookups fail, then assume the size of
362 * the memory block being realloc'd is the
363 * largest possible (so that all "nbytes" of new
364 * memory are copied into). Note that this could cause
365 * a memory fault if the old area was tiny, and the moon
366 * is gibbous. However, that is very unlikely.
368 if ((i = findbucket(op, 1)) < 0 &&
369 (i = findbucket(op, realloc_srchlen)) < 0)
373 if (onb < (u_int)pagesz)
374 onb -= sizeof (*op) + RSLOP;
376 onb += pagesz - sizeof (*op) - RSLOP;
377 /* avoid the copy if same size block */
382 i -= sizeof (*op) + RSLOP;
384 i += pagesz - sizeof (*op) - RSLOP;
386 if (nbytes <= onb && nbytes > (size_t)i) {
388 op->ov_size = (nbytes + RSLOP - 1) & ~(RSLOP - 1);
389 *(u_short *)((caddr_t)(op + 1) + op->ov_size) = RMAGIC;
395 if ((res = malloc(nbytes)) == NULL)
397 if (cp != res) /* common optimization if "compacting" */
398 bcopy(cp, res, (nbytes < onb) ? nbytes : onb);
403 * Search ``srchlen'' elements of each free list for a block whose
404 * header starts at ``freep''. If srchlen is -1 search the whole list.
405 * Return bucket number, or -1 if not found.
408 findbucket(freep, srchlen)
409 union overhead *freep;
412 register union overhead *p;
415 for (i = 0; i < NBUCKETS; i++) {
417 for (p = nextf[i]; p && j != srchlen; p = p->ov_next) {
428 * mstats - print out statistics about malloc
430 * Prints two lines of numbers, one showing the length of the free list
431 * for each size category, the second showing the number of mallocs -
432 * frees for each size category.
438 register union overhead *p;
442 fprintf(stderr, "Memory allocation statistics %s\nfree:\t", s);
443 for (i = 0; i < NBUCKETS; i++) {
444 for (j = 0, p = nextf[i]; p; p = p->ov_next, j++)
446 fprintf(stderr, " %d", j);
447 totfree += j * (1 << (i + 3));
449 fprintf(stderr, "\nused:\t");
450 for (i = 0; i < NBUCKETS; i++) {
451 fprintf(stderr, " %d", nmalloc[i]);
452 totused += nmalloc[i] * (1 << (i + 3));
454 fprintf(stderr, "\n\tTotal in use: %d, total free: %d\n",
468 fd = open(_PATH_DEVZERO, O_RDWR, 0);
470 perror(_PATH_DEVZERO);
473 if (pagepool_end - pagepool_start > pagesz) {
474 caddr_t addr = (caddr_t)
475 (((long)pagepool_start + pagesz - 1) & ~(pagesz - 1));
476 if (munmap(addr, pagepool_end - addr) != 0)
477 rtld_fdprintf(STDERR_FILENO, "morepages: munmap %p",
481 offset = (long)pagepool_start - ((long)pagepool_start & ~(pagesz - 1));
483 if ((pagepool_start = mmap(0, n * pagesz,
484 PROT_READ|PROT_WRITE,
485 MAP_ANON|MAP_COPY, fd, 0)) == (caddr_t)-1) {
486 rtld_printf("Cannot map anonymous memory\n");
489 pagepool_end = pagepool_start + n * pagesz;
490 pagepool_start += offset;