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Revert to first-best-fit run/chunk allocation.

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This effectively reverts 97c04a9383 (Use
first-fit rather than first-best-fit run/chunk allocation.).  In some
pathological cases, first-fit search dominates allocation time, and it
also tends not to converge as readily on a steady state of memory
layout, since precise allocation order has a bigger effect than for
first-best-fit.
This commit is contained in:
Jason Evans 2015-07-15 16:02:21 -07:00
parent 8693a9ea05
commit aa2826621e
3 changed files with 26 additions and 77 deletions
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57
src/arena.c
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@ -979,53 +979,28 @@ arena_chunk_ralloc_huge_expand(arena_t *arena, void *chunk, size_t oldsize,
return (err);
}
/* Do first-fit run selection. */
/*
* Do first-best-fit run selection, i.e. select the lowest run that best fits.
* Run sizes are quantized, so not all candidate runs are necessarily exactly
* the same size.
*/
static arena_run_t *
arena_run_first_fit(arena_t *arena, size_t size)
arena_run_first_best_fit(arena_t *arena, size_t size)
{
arena_run_t *run;
size_t search_size, max_size;
assert(size == s2u(size));
assert(size == PAGE_CEILING(size));
/*
* Iterate over all size classes that are at least large enough to
* satisfy the request, search for the lowest run of each size class,
* and choose the lowest of the runs found.
*/
run = NULL;
for (search_size = run_quantize_first(size), max_size =
run_quantize(arena_maxclass + large_pad); search_size <= max_size;
search_size = run_quantize_next(search_size)) {
arena_run_t *currun;
arena_chunk_t *currun_chunk;
size_t currun_pageind, currun_size;
arena_chunk_map_misc_t *key = (arena_chunk_map_misc_t *)
(search_size | CHUNK_MAP_KEY);
arena_chunk_map_misc_t *miscelm =
arena_avail_tree_nsearch(&arena->runs_avail, key);
if (miscelm == NULL)
break;
currun = &miscelm->run;
if (run == NULL || (uintptr_t)currun < (uintptr_t)run)
run = currun;
/* Skip iteration(s) if run is larger than the search size. */
currun_chunk = (arena_chunk_t *)CHUNK_ADDR2BASE(currun);
currun_pageind = arena_miscelm_to_pageind(miscelm);
currun_size = arena_mapbits_unallocated_size_get(currun_chunk,
currun_pageind);
assert(currun_size >= search_size);
search_size = currun_size;
}
return (run);
size_t search_size = run_quantize_first(size);
arena_chunk_map_misc_t *key = (arena_chunk_map_misc_t *)
(search_size | CHUNK_MAP_KEY);
arena_chunk_map_misc_t *miscelm =
arena_avail_tree_nsearch(&arena->runs_avail, key);
if (miscelm == NULL)
return (NULL);
return (&miscelm->run);
}
static arena_run_t *
arena_run_alloc_large_helper(arena_t *arena, size_t size, bool zero)
{
arena_run_t *run = arena_run_first_fit(arena, s2u(size));
arena_run_t *run = arena_run_first_best_fit(arena, s2u(size));
if (run != NULL)
arena_run_split_large(arena, run, size, zero);
return (run);
@ -1066,7 +1041,7 @@ arena_run_alloc_large(arena_t *arena, size_t size, bool zero)
static arena_run_t *
arena_run_alloc_small_helper(arena_t *arena, size_t size, index_t binind)
{
arena_run_t *run = arena_run_first_fit(arena, size);
arena_run_t *run = arena_run_first_best_fit(arena, size);
if (run != NULL)
arena_run_split_small(arena, run, size, binind);
return (run);