inc_node_lock_ref/dec_node_lock_ref adjusted evictable_size_ but did
not call _update_leaf_status, so nodes could become "phantoms" —
counted in evictable_size_ but missing from evictable_leaves. Under
load with write-behind, this caused eviction to return 0 despite
large evictable_size_, leading to OOM:
Available tokens: 778624 (evictable_size=706880)
evict_result=(num_tokens_evicted=0)
The race: write-behind locks node X via inc_node_lock_ref (X stays
in evictable_leaves). A request path touches X via inc_lock_ref,
which calls _update_leaf_status and removes X from evictable_leaves.
Request finishes, dec_lock_ref keeps X out (lock_ref still >0).
Write ack calls dec_node_lock_ref dropping lock_ref to 0, but never
calls _update_leaf_status — X is permanently lost.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
leavelet
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