From 8d532c51318bad2436880ecac972c9dfa3996c9b Mon Sep 17 00:00:00 2001 From: Eric Andersen Date: Tue, 30 Dec 2003 10:40:49 +0000 Subject: Rework malloc. The new default implementation is based on dlmalloc from Doug Lea. It is about 2x faster than the old malloc-930716, and behave itself much better -- it will properly release memory back to the system, and it uses a combination of brk() for small allocations and mmap() for larger allocations. -Erik --- libc/stdlib/malloc-standard/free.c | 382 +++++++++++++++++++++++++++++++++++++ 1 file changed, 382 insertions(+) create mode 100644 libc/stdlib/malloc-standard/free.c (limited to 'libc/stdlib/malloc-standard/free.c') diff --git a/libc/stdlib/malloc-standard/free.c b/libc/stdlib/malloc-standard/free.c new file mode 100644 index 000000000..4277767fa --- /dev/null +++ b/libc/stdlib/malloc-standard/free.c @@ -0,0 +1,382 @@ +/* + This is a version (aka dlmalloc) of malloc/free/realloc written by + Doug Lea and released to the public domain. Use, modify, and + redistribute this code without permission or acknowledgement in any + way you wish. Send questions, comments, complaints, performance + data, etc to dl@cs.oswego.edu + + VERSION 2.7.2 Sat Aug 17 09:07:30 2002 Doug Lea (dl at gee) + + Note: There may be an updated version of this malloc obtainable at + ftp://gee.cs.oswego.edu/pub/misc/malloc.c + Check before installing! + + Hacked up for uClibc by Erik Andersen +*/ + +#include "malloc.h" + + +/* ------------------------- __malloc_trim ------------------------- + __malloc_trim is an inverse of sorts to __malloc_alloc. It gives memory + back to the system (via negative arguments to sbrk) if there is unused + memory at the `high' end of the malloc pool. It is called automatically by + free() when top space exceeds the trim threshold. It is also called by the + public malloc_trim routine. It returns 1 if it actually released any + memory, else 0. +*/ +static int __malloc_trim(size_t pad, mstate av) +{ + long top_size; /* Amount of top-most memory */ + long extra; /* Amount to release */ + long released; /* Amount actually released */ + char* current_brk; /* address returned by pre-check sbrk call */ + char* new_brk; /* address returned by post-check sbrk call */ + size_t pagesz; + + pagesz = av->pagesize; + top_size = chunksize(av->top); + + /* Release in pagesize units, keeping at least one page */ + extra = ((top_size - pad - MINSIZE + (pagesz-1)) / pagesz - 1) * pagesz; + + if (extra > 0) { + + /* + Only proceed if end of memory is where we last set it. + This avoids problems if there were foreign sbrk calls. + */ + current_brk = (char*)(MORECORE(0)); + if (current_brk == (char*)(av->top) + top_size) { + + /* + Attempt to release memory. We ignore MORECORE return value, + and instead call again to find out where new end of memory is. + This avoids problems if first call releases less than we asked, + of if failure somehow altered brk value. (We could still + encounter problems if it altered brk in some very bad way, + but the only thing we can do is adjust anyway, which will cause + some downstream failure.) + */ + + MORECORE(-extra); + new_brk = (char*)(MORECORE(0)); + + if (new_brk != (char*)MORECORE_FAILURE) { + released = (long)(current_brk - new_brk); + + if (released != 0) { + /* Success. Adjust top. */ + av->sbrked_mem -= released; + set_head(av->top, (top_size - released) | PREV_INUSE); + check_malloc_state(); + return 1; + } + } + } + } + return 0; +} + +/* + Initialize a malloc_state struct. + + This is called only from within __malloc_consolidate, which needs + be called in the same contexts anyway. It is never called directly + outside of __malloc_consolidate because some optimizing compilers try + to inline it at all call points, which turns out not to be an + optimization at all. (Inlining it in __malloc_consolidate is fine though.) +*/ +static void malloc_init_state(mstate av) +{ + int i; + mbinptr bin; + + /* Establish circular links for normal bins */ + for (i = 1; i < NBINS; ++i) { + bin = bin_at(av,i); + bin->fd = bin->bk = bin; + } + + av->top_pad = DEFAULT_TOP_PAD; + av->n_mmaps_max = DEFAULT_MMAP_MAX; + av->mmap_threshold = DEFAULT_MMAP_THRESHOLD; + av->trim_threshold = DEFAULT_TRIM_THRESHOLD; + +#if MORECORE_CONTIGUOUS + set_contiguous(av); +#else + set_noncontiguous(av); +#endif + + + set_max_fast(av, DEFAULT_MXFAST); + + av->top = initial_top(av); + av->pagesize = malloc_getpagesize; +} + + +/* ---------------------------------------------------------------------- + * + * PUBLIC STUFF + * + * ----------------------------------------------------------------------*/ + + +/* ------------------------- __malloc_consolidate ------------------------- + + __malloc_consolidate is a specialized version of free() that tears + down chunks held in fastbins. Free itself cannot be used for this + purpose since, among other things, it might place chunks back onto + fastbins. So, instead, we need to use a minor variant of the same + code. + + Also, because this routine needs to be called the first time through + malloc anyway, it turns out to be the perfect place to trigger + initialization code. +*/ +void __malloc_consolidate(mstate av) +{ + mfastbinptr* fb; /* current fastbin being consolidated */ + mfastbinptr* maxfb; /* last fastbin (for loop control) */ + mchunkptr p; /* current chunk being consolidated */ + mchunkptr nextp; /* next chunk to consolidate */ + mchunkptr unsorted_bin; /* bin header */ + mchunkptr first_unsorted; /* chunk to link to */ + + /* These have same use as in free() */ + mchunkptr nextchunk; + size_t size; + size_t nextsize; + size_t prevsize; + int nextinuse; + mchunkptr bck; + mchunkptr fwd; + + /* + If max_fast is 0, we know that av hasn't + yet been initialized, in which case do so below + */ + + if (av->max_fast != 0) { + clear_fastchunks(av); + + unsorted_bin = unsorted_chunks(av); + + /* + Remove each chunk from fast bin and consolidate it, placing it + then in unsorted bin. Among other reasons for doing this, + placing in unsorted bin avoids needing to calculate actual bins + until malloc is sure that chunks aren't immediately going to be + reused anyway. + */ + + maxfb = &(av->fastbins[fastbin_index(av->max_fast)]); + fb = &(av->fastbins[0]); + do { + if ( (p = *fb) != 0) { + *fb = 0; + + do { + check_inuse_chunk(p); + nextp = p->fd; + + /* Slightly streamlined version of consolidation code in free() */ + size = p->size & ~PREV_INUSE; + nextchunk = chunk_at_offset(p, size); + nextsize = chunksize(nextchunk); + + if (!prev_inuse(p)) { + prevsize = p->prev_size; + size += prevsize; + p = chunk_at_offset(p, -((long) prevsize)); + unlink(p, bck, fwd); + } + + if (nextchunk != av->top) { + nextinuse = inuse_bit_at_offset(nextchunk, nextsize); + set_head(nextchunk, nextsize); + + if (!nextinuse) { + size += nextsize; + unlink(nextchunk, bck, fwd); + } + + first_unsorted = unsorted_bin->fd; + unsorted_bin->fd = p; + first_unsorted->bk = p; + + set_head(p, size | PREV_INUSE); + p->bk = unsorted_bin; + p->fd = first_unsorted; + set_foot(p, size); + } + + else { + size += nextsize; + set_head(p, size | PREV_INUSE); + av->top = p; + } + + } while ( (p = nextp) != 0); + + } + } while (fb++ != maxfb); + } + else { + malloc_init_state(av); + check_malloc_state(); + } +} + + +/* ------------------------------ free ------------------------------ */ +void free(void* mem) +{ + mstate av; + + mchunkptr p; /* chunk corresponding to mem */ + size_t size; /* its size */ + mfastbinptr* fb; /* associated fastbin */ + mchunkptr nextchunk; /* next contiguous chunk */ + size_t nextsize; /* its size */ + int nextinuse; /* true if nextchunk is used */ + size_t prevsize; /* size of previous contiguous chunk */ + mchunkptr bck; /* misc temp for linking */ + mchunkptr fwd; /* misc temp for linking */ + + /* free(0) has no effect */ + if (mem == NULL) + return; + + LOCK; + av = get_malloc_state(); + p = mem2chunk(mem); + size = chunksize(p); + + check_inuse_chunk(p); + + /* + If eligible, place chunk on a fastbin so it can be found + and used quickly in malloc. + */ + + if ((unsigned long)(size) <= (unsigned long)(av->max_fast) + +#if TRIM_FASTBINS + /* If TRIM_FASTBINS set, don't place chunks + bordering top into fastbins */ + && (chunk_at_offset(p, size) != av->top) +#endif + ) { + + set_fastchunks(av); + fb = &(av->fastbins[fastbin_index(size)]); + p->fd = *fb; + *fb = p; + } + + /* + Consolidate other non-mmapped chunks as they arrive. + */ + + else if (!chunk_is_mmapped(p)) { + set_anychunks(av); + + nextchunk = chunk_at_offset(p, size); + nextsize = chunksize(nextchunk); + + /* consolidate backward */ + if (!prev_inuse(p)) { + prevsize = p->prev_size; + size += prevsize; + p = chunk_at_offset(p, -((long) prevsize)); + unlink(p, bck, fwd); + } + + if (nextchunk != av->top) { + /* get and clear inuse bit */ + nextinuse = inuse_bit_at_offset(nextchunk, nextsize); + set_head(nextchunk, nextsize); + + /* consolidate forward */ + if (!nextinuse) { + unlink(nextchunk, bck, fwd); + size += nextsize; + } + + /* + Place the chunk in unsorted chunk list. Chunks are + not placed into regular bins until after they have + been given one chance to be used in malloc. + */ + + bck = unsorted_chunks(av); + fwd = bck->fd; + p->bk = bck; + p->fd = fwd; + bck->fd = p; + fwd->bk = p; + + set_head(p, size | PREV_INUSE); + set_foot(p, size); + + check_free_chunk(p); + } + + /* + If the chunk borders the current high end of memory, + consolidate into top + */ + + else { + size += nextsize; + set_head(p, size | PREV_INUSE); + av->top = p; + check_chunk(p); + } + + /* + If freeing a large space, consolidate possibly-surrounding + chunks. Then, if the total unused topmost memory exceeds trim + threshold, ask malloc_trim to reduce top. + + Unless max_fast is 0, we don't know if there are fastbins + bordering top, so we cannot tell for sure whether threshold + has been reached unless fastbins are consolidated. But we + don't want to consolidate on each free. As a compromise, + consolidation is performed if FASTBIN_CONSOLIDATION_THRESHOLD + is reached. + */ + + if ((unsigned long)(size) >= FASTBIN_CONSOLIDATION_THRESHOLD) { + if (have_fastchunks(av)) + __malloc_consolidate(av); + + if ((unsigned long)(chunksize(av->top)) >= + (unsigned long)(av->trim_threshold)) + __malloc_trim(av->top_pad, av); + } + + } + /* + If the chunk was allocated via mmap, release via munmap() + Note that if HAVE_MMAP is false but chunk_is_mmapped is + true, then user must have overwritten memory. There's nothing + we can do to catch this error unless DEBUG is set, in which case + check_inuse_chunk (above) will have triggered error. + */ + + else { + int ret; + size_t offset = p->prev_size; + av->n_mmaps--; + av->mmapped_mem -= (size + offset); + ret = munmap((char*)p - offset, size + offset); + /* munmap returns non-zero on failure */ + assert(ret == 0); + } + UNLOCK; +} + -- cgit v1.2.3