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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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src/emap.c
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@@ -50,7 +50,8 @@ emap_try_acquire_edata_neighbor_impl(tsdn_t *tsdn, emap_t *emap, edata_t *edata,
assert(!edata_state_in_transition(expected_state));
assert(expected_state == extent_state_dirty
|| expected_state == extent_state_muzzy
|| expected_state == extent_state_retained);
|| expected_state == extent_state_retained
|| expected_state == extent_state_pinned);
void *neighbor_addr = forward ? edata_past_get(edata)
: edata_before_get(edata);