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Tweak chunk purge order according to fragmentation.

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Tweak chunk purge order to purge unfragmented chunks from high to low
memory.  This facilitates dirty run reuse.
This commit is contained in:
Jason Evans 2012-11-07 10:05:04 -08:00
parent ed90c97332
commit abf6739317
1 changed files with 34 additions and 11 deletions
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37
src/arena.c
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@ -138,14 +138,22 @@ rb_gen(static UNUSED, arena_avail_tree_, arena_avail_tree_t, arena_chunk_map_t,
static inline int static inline int
arena_chunk_dirty_comp(arena_chunk_t *a, arena_chunk_t *b) arena_chunk_dirty_comp(arena_chunk_t *a, arena_chunk_t *b)
{ {
size_t a_val, b_val;
assert(a != NULL); assert(a != NULL);
assert(b != NULL); assert(b != NULL);
/*
* Short-circuit for self comparison. The following comparison code
* would come to the same result, but at the cost of executing the slow
* path.
*/
if (a == b)
return (0);
/* /*
* Order such that chunks with higher fragmentation are "less than" * Order such that chunks with higher fragmentation are "less than"
* those with lower fragmentation. Fragmentation is measured as: * those with lower fragmentation -- purging order is from "least" to
* "greatest". Fragmentation is measured as:
* *
* mean current avail run size * mean current avail run size
* -------------------------------- * --------------------------------
@ -163,18 +171,33 @@ arena_chunk_dirty_comp(arena_chunk_t *a, arena_chunk_t *b)
* comparison, in order to avoid division. * comparison, in order to avoid division.
* *
*/ */
a_val = (a->nruns_avail - a->nruns_adjac) * b->nruns_avail; {
b_val = (b->nruns_avail - b->nruns_adjac) * a->nruns_avail; size_t a_val = (a->nruns_avail - a->nruns_adjac) *
b->nruns_avail;
size_t b_val = (b->nruns_avail - b->nruns_adjac) *
a->nruns_avail;
if (a_val < b_val) if (a_val < b_val)
return (1); return (1);
if (a_val > b_val) if (a_val > b_val)
return (-1); return (-1);
/* Break ties by chunk address. */ }
/*
* Break ties by chunk address. For fragmented chunks, report lower
* addresses as "lower", so that fragmentation reduction happens first
* at lower addresses. However, use the opposite ordering for
* unfragmented chunks, in order to increase the chances of
* re-allocating dirty runs.
*/
{ {
uintptr_t a_chunk = (uintptr_t)a; uintptr_t a_chunk = (uintptr_t)a;
uintptr_t b_chunk = (uintptr_t)b; uintptr_t b_chunk = (uintptr_t)b;
int ret = ((a_chunk > b_chunk) - (a_chunk < b_chunk));
return ((a_chunk > b_chunk) - (a_chunk < b_chunk)); if (a->nruns_adjac == 0) {
assert(b->nruns_adjac == 0);
ret = -ret;
}
return (ret);
} }
} }