jemalloc 5.4.0 is now available, containing over 160 commits focused on technical debt cleaning, refactorings, bug fixes, test coverage improvements, and option cleanups. The release also addresses portability issues reported upstream.

New features include the addition of EXTENT_ALLOC_FLAG_PINNED, allowing custom extent-allocation hooks to mark non-reclaimable mappings like Huge TLB pages for preferential reuse outside the decay and purge pipeline. Several mallctl interfaces were introduced to report pinned-memory usage and mutex statistics, including stats.pinned, stats.arenas.<i>.pinned, and related counters.

Incompatible changes adapt tcache fill and retention targets per bin based on observed demand between GC events, replacing the previous fixed refill/flush policy. Seven legacy non-experimental controls were removed, though tcache_ncached_max remains supported.

Bug fixes preserve errno across free operations and process_madvise-based page purging, correct numeric overflow checks in size classes, and address TSD lifecycle edge cases. Optimizations modularize the front end, simplify ctl dispatch, and refactor statistics collection. Contributors include @spredolac, @Algunenano, @binliu19, @bigbruno, @fzakaria, @ibookstein, @guangli-dai, and @gctony.