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Fix a bug in lazy deallocation that was introduced when

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arena_dalloc_lazy_hard() was split out of arena_dalloc_lazy() in revision
1.162.

Reduce thundering herd problems in lazy deallocation by randomly varying
how many probes a thread does before taking the slow path.
This commit is contained in:
Jason Evans 2008-02-08 08:02:34 +00:00
parent fbe8fb4d7b
commit 157d89fe25
Notes: svn2git 2020-12-20 02:59:44 +00:00 
svn path=/head/; revision=176103
1 changed files with 10 additions and 7 deletions
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17
lib/libc/stdlib/malloc.c
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@ -315,7 +315,8 @@ __FBSDID("$FreeBSD$");
* trials (each deallocation is a trial), so the actual average threshold
* for clearing the cache is somewhat lower.
*/
# define LAZY_FREE_NPROBES 5
# define LAZY_FREE_NPROBES_2POW_MIN 2
# define LAZY_FREE_NPROBES_2POW_MAX 3
#endif
/*
@ -931,7 +932,7 @@ static void *arena_palloc(arena_t *arena, size_t alignment, size_t size,
static size_t arena_salloc(const void *ptr);
#ifdef MALLOC_LAZY_FREE
static void arena_dalloc_lazy_hard(arena_t *arena, arena_chunk_t *chunk,
void *ptr, size_t pageind, arena_chunk_map_t *mapelm);
void *ptr, size_t pageind, arena_chunk_map_t *mapelm, unsigned slot);
#endif
static void arena_dalloc_large(arena_t *arena, arena_chunk_t *chunk,
void *ptr);
@ -3348,7 +3349,7 @@ arena_dalloc_lazy(arena_t *arena, arena_chunk_t *chunk, void *ptr,
size_t pageind, arena_chunk_map_t *mapelm)
{
void **free_cache = arena->free_cache;
unsigned i, slot;
unsigned i, nprobes, slot;
if (__isthreaded == false || opt_lazy_free_2pow < 0) {
malloc_spin_lock(&arena->lock);
@ -3357,7 +3358,9 @@ arena_dalloc_lazy(arena_t *arena, arena_chunk_t *chunk, void *ptr,
return;
}
for (i = 0; i < LAZY_FREE_NPROBES; i++) {
nprobes = (1U << LAZY_FREE_NPROBES_2POW_MIN) + PRN(lazy_free,
(LAZY_FREE_NPROBES_2POW_MAX - LAZY_FREE_NPROBES_2POW_MIN));
for (i = 0; i < nprobes; i++) {
slot = PRN(lazy_free, opt_lazy_free_2pow);
if (atomic_cmpset_ptr((uintptr_t *)&free_cache[slot],
(uintptr_t)NULL, (uintptr_t)ptr)) {
@ -3365,15 +3368,15 @@ arena_dalloc_lazy(arena_t *arena, arena_chunk_t *chunk, void *ptr,
}
}
arena_dalloc_lazy_hard(arena, chunk, ptr, pageind, mapelm);
arena_dalloc_lazy_hard(arena, chunk, ptr, pageind, mapelm, slot);
}
static void
arena_dalloc_lazy_hard(arena_t *arena, arena_chunk_t *chunk, void *ptr,
size_t pageind, arena_chunk_map_t *mapelm)
size_t pageind, arena_chunk_map_t *mapelm, unsigned slot)
{
void **free_cache = arena->free_cache;
unsigned i, slot;
unsigned i;
malloc_spin_lock(&arena->lock);
arena_dalloc_small(arena, chunk, ptr, pageind, *mapelm);