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Introduce pinned extents to contain unpurgeable pages

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Some pages (e.g., hugetlb pages) cannot be purged, and should be
prioritized for reuse.  A custom extent_alloc hook signals this by
OR'ing EXTENT_ALLOC_FLAG_PINNED into the low bits of the returned
pointer; jemalloc strips the flag bits and caches pinned extents in
a dedicated ecache_pinned, separate from the dirty/muzzy decay
pipeline.

Pinned extents do not coalesce eagerly, except for ones larger than
SC_LARGE_MINCLASS.  A prefer-small policy reuses the smallest fitting
pinned extent, to avoid unnecessary split/fragmentation.
This commit is contained in:
Bin Liu 2026-04-19 22:56:22 -07:00 • committed by Guangli Dai
parent 7638093c73
commit be2de8ccd8
22 changed files with 977 additions and 86 deletions
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17
src/pa_extra.c
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@ -34,6 +34,7 @@ pa_shard_prefork4(tsdn_t *tsdn, pa_shard_t *shard) {
ecache_prefork(tsdn, &shard->pac.ecache_dirty);
ecache_prefork(tsdn, &shard->pac.ecache_muzzy);
ecache_prefork(tsdn, &shard->pac.ecache_retained);
ecache_prefork(tsdn, &shard->pac.ecache_pinned);
if (shard->ever_used_hpa) {
hpa_shard_prefork4(tsdn, &shard->hpa_shard);
}
@ -50,6 +51,7 @@ pa_shard_postfork_parent(tsdn_t *tsdn, pa_shard_t *shard) {
ecache_postfork_parent(tsdn, &shard->pac.ecache_dirty);
ecache_postfork_parent(tsdn, &shard->pac.ecache_muzzy);
ecache_postfork_parent(tsdn, &shard->pac.ecache_retained);
ecache_postfork_parent(tsdn, &shard->pac.ecache_pinned);
malloc_mutex_postfork_parent(tsdn, &shard->pac.grow_mtx);
malloc_mutex_postfork_parent(tsdn, &shard->pac.decay_dirty.mtx);
malloc_mutex_postfork_parent(tsdn, &shard->pac.decay_muzzy.mtx);
@ -64,6 +66,7 @@ pa_shard_postfork_child(tsdn_t *tsdn, pa_shard_t *shard) {
ecache_postfork_child(tsdn, &shard->pac.ecache_dirty);
ecache_postfork_child(tsdn, &shard->pac.ecache_muzzy);
ecache_postfork_child(tsdn, &shard->pac.ecache_retained);
ecache_postfork_child(tsdn, &shard->pac.ecache_pinned);
malloc_mutex_postfork_child(tsdn, &shard->pac.grow_mtx);
malloc_mutex_postfork_child(tsdn, &shard->pac.decay_dirty.mtx);
malloc_mutex_postfork_child(tsdn, &shard->pac.decay_muzzy.mtx);
@ -107,12 +110,15 @@ pa_shard_stats_merge(tsdn_t *tsdn, pa_shard_t *shard,
pa_shard_stats_out->pac_stats.retained +=
ecache_npages_get(&shard->pac.ecache_retained) << LG_PAGE;
pa_shard_stats_out->pac_stats.pinned +=
ecache_npages_get(&shard->pac.ecache_pinned) << LG_PAGE;
pa_shard_stats_out->edata_avail += atomic_load_zu(
&shard->edata_cache.count, ATOMIC_RELAXED);
size_t resident_pgs = 0;
resident_pgs += pa_shard_nactive(shard);
resident_pgs += pa_shard_ndirty(shard);
resident_pgs += ecache_npages_get(&shard->pac.ecache_pinned);
*resident += (resident_pgs << LG_PAGE);
/* Dirty decay stats */
@ -147,22 +153,27 @@ pa_shard_stats_merge(tsdn_t *tsdn, pa_shard_t *shard,
atomic_load_zu(&shard->pac.stats->abandoned_vm, ATOMIC_RELAXED));
for (pszind_t i = 0; i < SC_NPSIZES; i++) {
size_t dirty, muzzy, retained, dirty_bytes, muzzy_bytes,
retained_bytes;
size_t dirty, muzzy, retained, pinned, dirty_bytes,
muzzy_bytes, retained_bytes, pinned_bytes;
dirty = ecache_nextents_get(&shard->pac.ecache_dirty, i);
muzzy = ecache_nextents_get(&shard->pac.ecache_muzzy, i);
retained = ecache_nextents_get(&shard->pac.ecache_retained, i);
pinned = ecache_nextents_get(&shard->pac.ecache_pinned, i);
dirty_bytes = ecache_nbytes_get(&shard->pac.ecache_dirty, i);
muzzy_bytes = ecache_nbytes_get(&shard->pac.ecache_muzzy, i);
retained_bytes = ecache_nbytes_get(
&shard->pac.ecache_retained, i);
pinned_bytes = ecache_nbytes_get(
&shard->pac.ecache_pinned, i);
estats_out[i].ndirty = dirty;
estats_out[i].nmuzzy = muzzy;
estats_out[i].nretained = retained;
estats_out[i].npinned = pinned;
estats_out[i].dirty_bytes = dirty_bytes;
estats_out[i].muzzy_bytes = muzzy_bytes;
estats_out[i].retained_bytes = retained_bytes;
estats_out[i].pinned_bytes = pinned_bytes;
}
if (shard->ever_used_hpa) {
@ -189,6 +200,8 @@ pa_shard_mtx_stats_read(tsdn_t *tsdn, pa_shard_t *shard,
&shard->pac.ecache_muzzy.mtx, arena_prof_mutex_extents_muzzy);
pa_shard_mtx_stats_read_single(tsdn, mutex_prof_data,
&shard->pac.ecache_retained.mtx, arena_prof_mutex_extents_retained);
pa_shard_mtx_stats_read_single(tsdn, mutex_prof_data,
&shard->pac.ecache_pinned.mtx, arena_prof_mutex_extents_pinned);
pa_shard_mtx_stats_read_single(tsdn, mutex_prof_data,
&shard->pac.decay_dirty.mtx, arena_prof_mutex_decay_dirty);
pa_shard_mtx_stats_read_single(tsdn, mutex_prof_data,