Jemalloc 5.4.0 lands with 160+ commits: pinned-memory tracking, tcache cleanup, deadlock fixes

Jemalloc, the widely deployed general-purpose memory allocator, shipped version 5.4.0 on September 17, 2024, folding in more than 160 commits. The release leans heavily toward maintenance rather than headline features: a large refactoring pass that modularized the allocator’s front end, untangled tcache and arena ownership, added an OS abstraction layer, and removed the PAI vtable dispatch to simplify page-allocation boundaries. Alongside the internal cleanup, it retires several long-standing tuning options.

The notable functional additions are targeted at systems and performance work. A new EXTENT_ALLOC_FLAG_PINNED marks non-reclaimable mappings such as HugeTLB pages so they get preferential reuse, backed by new mallctl interfaces that report pinned-memory usage. Per-CPU arena selection can now be resumed through thread.arena, human-readable and JSON stats output were brought into closer alignment, and C++ infallible-new moved from a runtime setting to a compile-time —enable-cxx-infallible-new flag. Operators should note an incompatible change: seven legacy tcache controls (including lg_tcache_nslots_mul and the flush-div knobs) are gone and now silently ignored, so any configs relying on them will quietly lose effect.

The bug fixes matter most for correctness-sensitive deployments. This release preserves errno across free() and purging, fixes numeric overflow in size-class checks, corrects NULL handling in free_sized() and free_aligned_sized() for C23 compliance, resolves thread-teardown and TSD lifecycle edge cases, and closes a potential deadlock during arena_reset plus a prof-sampling/guard-page interaction bug. For the many databases, runtimes, and language toolchains that link jemalloc, the deadlock and errno fixes alone are reason to track this version.