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Fix # of unpurged pages in decay algorithm.

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When # of dirty pages move below npages_limit (e.g. they are reused), we should
not lower number of unpurged pages because that would cause the reused pages to
be double counted in the backlog (as a result, decay happen slower than it
should).  Instead, set number of unpurged to the greater of current npages and
npages_limit.

Added an assertion: the ceiling # of pages should be greater than npages_limit.
This commit is contained in:
Qi Wang 2017-05-22 13:09:17 -07:00 committed by Qi Wang
parent 0eae838b0d
commit eeefdf3ce8
2 changed files with 29 additions and 11 deletions
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2
include/jemalloc/internal/arena_structs_b.h
View File

@ -103,6 +103,8 @@ struct arena_decay_s {
* *
* Synchronization: Same as associated arena's stats field. */ * Synchronization: Same as associated arena's stats field. */
decay_stats_t *stats; decay_stats_t *stats;
/* Peak number of pages in associated extents. Used for debug only. */
uint64_t ceil_npages;
}; };
struct arena_bin_s { struct arena_bin_s {

38
src/arena.c
View File

@ -639,6 +639,17 @@ arena_decay_backlog_update_last(arena_decay_t *decay, extents_t *extents) {
size_t ndirty_delta = (ndirty > decay->nunpurged) ? ndirty - size_t ndirty_delta = (ndirty > decay->nunpurged) ? ndirty -
decay->nunpurged : 0; decay->nunpurged : 0;
decay->backlog[SMOOTHSTEP_NSTEPS-1] = ndirty_delta; decay->backlog[SMOOTHSTEP_NSTEPS-1] = ndirty_delta;
if (config_debug) {
if (ndirty > decay->ceil_npages) {
decay->ceil_npages = ndirty;
}
size_t npages_limit = arena_decay_backlog_npages_limit(decay);
assert(decay->ceil_npages >= npages_limit);
if (decay->ceil_npages > npages_limit) {
decay->ceil_npages = npages_limit;
}
}
} }
static void static void
@ -664,11 +675,9 @@ arena_decay_backlog_update(arena_decay_t *decay, extents_t *extents,
} }
static void static void
arena_decay_try_purge(tsdn_t *tsdn, arena_t *arena, arena_decay_try_purge(tsdn_t *tsdn, arena_t *arena, arena_decay_t *decay,
arena_decay_t *decay, extents_t *extents) { extents_t *extents, size_t current_npages, size_t npages_limit) {
size_t npages_limit = arena_decay_backlog_npages_limit(decay); if (current_npages > npages_limit) {
if (extents_npages_get(extents) > npages_limit) {
arena_decay_to_limit(tsdn, arena, decay, extents, false, arena_decay_to_limit(tsdn, arena, decay, extents, false,
npages_limit); npages_limit);
} }
@ -702,16 +711,20 @@ static void
arena_decay_epoch_advance(tsdn_t *tsdn, arena_t *arena, arena_decay_t *decay, arena_decay_epoch_advance(tsdn_t *tsdn, arena_t *arena, arena_decay_t *decay,
extents_t *extents, const nstime_t *time, bool purge) { extents_t *extents, const nstime_t *time, bool purge) {
arena_decay_epoch_advance_helper(decay, extents, time); arena_decay_epoch_advance_helper(decay, extents, time);
if (purge) {
arena_decay_try_purge(tsdn, arena, decay, extents);
}
size_t current_npages = extents_npages_get(extents);
size_t npages_limit = arena_decay_backlog_npages_limit(decay);
if (purge) {
arena_decay_try_purge(tsdn, arena, decay, extents,
current_npages, npages_limit);
}
/* /*
* There may be concurrent ndirty fluctuation between the purge above * There may be concurrent ndirty fluctuation between the purge above
* and the nunpurged update below, but this is inconsequential to decay * and the nunpurged update below, but this is inconsequential to decay
* machinery correctness. * machinery correctness.
*/ */
decay->nunpurged = extents_npages_get(extents); decay->nunpurged = (npages_limit > current_npages) ? npages_limit :
current_npages;
} }
static void static void
@ -727,7 +740,7 @@ arena_decay_reinit(arena_decay_t *decay, extents_t *extents, ssize_t decay_ms) {
nstime_update(&decay->epoch); nstime_update(&decay->epoch);
decay->jitter_state = (uint64_t)(uintptr_t)decay; decay->jitter_state = (uint64_t)(uintptr_t)decay;
arena_decay_deadline_init(decay); arena_decay_deadline_init(decay);
decay->nunpurged = extents_npages_get(extents); decay->nunpurged = 0;
memset(decay->backlog, 0, SMOOTHSTEP_NSTEPS * sizeof(size_t)); memset(decay->backlog, 0, SMOOTHSTEP_NSTEPS * sizeof(size_t));
} }
@ -738,6 +751,7 @@ arena_decay_init(arena_decay_t *decay, extents_t *extents, ssize_t decay_ms,
for (size_t i = 0; i < sizeof(arena_decay_t); i++) { for (size_t i = 0; i < sizeof(arena_decay_t); i++) {
assert(((char *)decay)[i] == 0); assert(((char *)decay)[i] == 0);
} }
decay->ceil_npages = 0;
} }
if (malloc_mutex_init(&decay->mtx, "decay", WITNESS_RANK_DECAY, if (malloc_mutex_init(&decay->mtx, "decay", WITNESS_RANK_DECAY,
malloc_mutex_rank_exclusive)) { malloc_mutex_rank_exclusive)) {
@ -814,7 +828,9 @@ arena_maybe_decay(tsdn_t *tsdn, arena_t *arena, arena_decay_t *decay,
arena_decay_epoch_advance(tsdn, arena, decay, extents, &time, arena_decay_epoch_advance(tsdn, arena, decay, extents, &time,
should_purge); should_purge);
} else if (is_background_thread) { } else if (is_background_thread) {
arena_decay_try_purge(tsdn, arena, decay, extents); arena_decay_try_purge(tsdn, arena, decay, extents,
extents_npages_get(extents),
arena_decay_backlog_npages_limit(decay));
} }
return advance_epoch; return advance_epoch;