--- title: "jemalloc 5.4.0" slug: jemalloc-5-4-0 url: https://listedarticles.com/articles/jemalloc-5-4-0 canonical_url: https://github.com/jemalloc/jemalloc/releases/tag/5.4.0 content_type: changelog language: en published_at: 2026-09-18T09:14:17.659Z updated_at: 2026-09-18T09:14:17.659Z authored_by: human publisher: "jemalloc" publisher_url: https://github.com/jemalloc/jemalloc topics: ["Systems Programming", "Performance", "Open Source", "C"] license: all-rights-reserved word_count: 762 reading_minutes: 3 citation: "jemalloc. \"jemalloc 5.4.0.\" 18 Sept 2026. https://github.com/jemalloc/jemalloc/releases/tag/5.4.0 (all-rights-reserved)" # The full text follows. The web page shows an extract and sends readers # to the source above; quote the citation and link the canonical URL. --- # jemalloc 5.4.0 > Release notes for jemalloc 5.4.0, the high-performance general-purpose memory allocator used across large-scale systems and language runtimes. [ jemalloc ](/jemalloc) / **[jemalloc](/jemalloc/jemalloc) ** Public * [ Fork 1.6k ](/login?return_to=%2Fjemalloc%2Fjemalloc) * [ Star 11.1k ](/login?return_to=%2Fjemalloc%2Fjemalloc) # 5.4.0 [Latest](/jemalloc/jemalloc/releases/latest) [Latest](/jemalloc/jemalloc/releases/latest) Compare # Choose a tag to compare ## Sorry, something went wrong. Filter Loading ## Sorry, something went wrong. ### Uh oh! There was an error while loading. [Please reload this page](). ## No results found [View all tags](/jemalloc/jemalloc/tags) [guangli-dai](/guangli-dai) released this 17 Sep 18:31 ยท [ 5 commits ](/jemalloc/jemalloc/compare/5.4.0...dev) to dev since this release [ 5.4.0 ](/jemalloc/jemalloc/tree/5.4.0) [ `7a34f18`](/jemalloc/jemalloc/commit/7a34f18502e7b222724097cdcd499b437d189acc) This release contains over 160 commits, focusing on the technical debts cleaning including refactorings, bug fixes, test coverage improvement, and option cleanups. The release also includes portability improvements per upstream issues report. New features: * Add `EXTENT_ALLOC_FLAG_PINNED` so custom extent-allocation hooks can mark non-reclaimable mappings, such as HugeTLB pages, for preferential reuse outside the decay and purge pipeline. Add the mallctl interfaces `stats.pinned`, `stats.arenas..pinned`, `stats.arenas..extents..npinned`, `stats.arenas..extents..pinned_bytes`, and `stats.arenas..mutexes.extents_pinned.{counter}` to report pinned-memory usage and mutex statistics. ([@binliu19](https://github.com/binliu19): [`be2de8c`](https://github.com/jemalloc/jemalloc/commit/be2de8ccd8ba38d687647ed43d75dc0ee5846df7)) * Allow resuming per-CPU arena selection via `thread.arena`. ([@Algunenano](https://github.com/Algunenano): [`68c35f6`](https://github.com/jemalloc/jemalloc/commit/68c35f655792f40243ba5f4bc9577e03cc7cc49d)) * Better align the contents of human-readable and JSON malloc statistics. ([@spredolac](https://github.com/spredolac): [`68fe1be`](https://github.com/jemalloc/jemalloc/commit/68fe1be1ad3cd8007a9404a199155d16f5835d08), [`30b1a41`](https://github.com/jemalloc/jemalloc/commit/30b1a41042b06980a1bd1dfb5235dc3026e618ae), [`04aad97`](https://github.com/jemalloc/jemalloc/commit/04aad97faafcb4f15125d4fbd6e92f7fd0aec323)) * Replace the runtime `experimental_infallible_new` option with the compile-time `--enable-cxx-infallible-new` option, enabling compiler-level optimizations and optimization in move constructors, and fix the `new(std::nothrow)` contract ([@spredolac](https://github.com/spredolac): [`160ab9d`](https://github.com/jemalloc/jemalloc/commit/160ab9d7f62aca5a930929899a9b3be0e459fd83), [`fe33667`](https://github.com/jemalloc/jemalloc/commit/fe336672309b724764093bff8253276bd600ce27)) Incompatible changes: * Adapt tcache fill and retention targets per bin to demand observed between GC events, replacing the fixed refill/flush policy. Remove seven legacy non-experimental controls: `lg_tcache_nslots_mul`, `tcache_nslots_small_min`, `tcache_nslots_small_max`, `tcache_nslots_large`, `tcache_gc_delay_bytes`, `lg_tcache_flush_small_div`, and `lg_tcache_flush_large_div`. Corresponding `malloc_conf` settings are silently ignored, matching `opt.*` mallctls return ENOENT, and `tcache_ncached_max` remains supported. ([@spredolac](https://github.com/spredolac): [`d13fe91`](https://github.com/jemalloc/jemalloc/commit/d13fe91afd6f2834fef5f3eb320f5f7fe34de7be)) Bug fixes: * Preserve `errno` across `free`, `free_sized`, and `free_aligned_sized`, and across `process_madvise`-based page purging. ([@spredolac](https://github.com/spredolac): [`3a77966`](https://github.com/jemalloc/jemalloc/commit/3a77966168b3c48437370e75e33159980e0fac89), [`86f0582`](https://github.com/jemalloc/jemalloc/commit/86f058287faae50caeb6d785aaca0dbb1f1e62b2)) * Fix numeric overflow checks in size classes. ([@spredolac](https://github.com/spredolac): [`6b24522`](https://github.com/jemalloc/jemalloc/commit/6b245225459fd09132c877b83a91725cb56097da)) * Accept NULL in `free_sized()` and `free_aligned_sized()` (C23 correctness). ([@bigbruno](https://github.com/bigbruno): [`7ce8b91`](https://github.com/jemalloc/jemalloc/commit/7ce8b9165d342e705b4554dcc991ec0d41ae36f6)) * Fix TSD lifecycle edge cases by 1) initializing thread-cache bins before marking the cache enabled, preventing reentrant bootstrap allocations from using uninitialized state, and 2) avoiding TSD recreation for late deallocations after thread teardown on generic-TSD platforms. ([@fzakaria](https://github.com/fzakaria): [`54f22c8`](https://github.com/jemalloc/jemalloc/commit/54f22c83d8f649f5c34d1b4d89050e00c631a32e), [@spredolac](https://github.com/spredolac): [`fb5499a`](https://github.com/jemalloc/jemalloc/commit/fb5499aa9c13aa7c0e11041009ae894c584b64bd)) * Use `O_CLOEXEC` when opening the THP sysfs file in `init_thp_state`. ([@ibookstein](https://github.com/ibookstein): [`d070554`](https://github.com/jemalloc/jemalloc/commit/d0705543e0b3733b12e8643a3962b77834b24209)) * Fix duplicate `opt.stats_print` and `opt.stats_print_opts` fields in `malloc_stats_print` output. ([@spredolac](https://github.com/spredolac): [`dfe3a2e`](https://github.com/jemalloc/jemalloc/commit/dfe3a2ed5f668f39474d6e174b0d41db80fa33dc)) * Fix a potential deadlock during `arena_reset`. ([@guangli-dai](https://github.com/guangli-dai): [`6957341`](https://github.com/jemalloc/jemalloc/commit/6957341f190b8c66a197e181d5f413d4c77526c2)) * Fix a prof-sampling / guard-page interaction bug in the SAN. ([@gctony](https://github.com/gctony): [`e36a0fa`](https://github.com/jemalloc/jemalloc/commit/e36a0fa5bc1e1090362505ac4af4408466ba5163)) Optimizations and refactors: * Modularize jemalloc's front end by extracting arena management, initialization, fork orchestration, and allocation dispatch from `jemalloc.c`; untangle tcache/arena ownership; and consolidate the internal header graph to eliminate circular dependencies. ([@spredolac](https://github.com/spredolac): [`ba1e2fe`](https://github.com/jemalloc/jemalloc/commit/ba1e2fe4db78911a56d254e1bd69e17233dde61b), [`8874597`](https://github.com/jemalloc/jemalloc/commit/88745978e91d323aa87fdab7e9f33d5bc50bff57), [`9d75722`](https://github.com/jemalloc/jemalloc/commit/9d75722344244dcdb4a29fc1875081b9fcc95f1f), [`de9ad14`](https://github.com/jemalloc/jemalloc/commit/de9ad1450b09a09732195a1e66c0321d8b077d1e), ...) * Simplify ctl dispatch by refactoring arena helpers, internalizing an implementation-only control, replacing control-flow macros with typed helpers, and organizing `ctl.c` by subsystem. ([@spredolac](https://github.com/spredolac): [`9e14346`](https://github.com/jemalloc/jemalloc/commit/9e143468a244465e4b4a3822f4c1d8de42f39335), [`901365d`](https://github.com/jemalloc/jemalloc/commit/901365d473f4fe4ac3023946a56973f0753c18a3), [`4e903a0`](https://github.com/jemalloc/jemalloc/commit/4e903a0a32ba278085f5050ee13442b8e4d2e844), [`5bc8d6e`](https://github.com/jemalloc/jemalloc/commit/5bc8d6e9e21dd7369b8f7899680620578977500a)) * Cap the base-block growth heuristic to avoid virtual-memory exhaustion under rare racy conditions. ([@guangli-dai](https://github.com/guangli-dai): [`2f4db8c`](https://github.com/jemalloc/jemalloc/commit/2f4db8cf5dad7f53164bef13a2c5b49e1195d042)) * Move background-thread lifecycle and state operations into the background-thread module, clarifying ownership independently of PAC/HPA callers. ([@guangli-dai](https://github.com/guangli-dai): [`f1f0792`](https://github.com/jemalloc/jemalloc/commit/f1f07923707fb98b7bfd5d837c88dfdd385ba8ce)) * Simplify the page-allocation boundary by replacing PAI vtable dispatch with direct PAC/HPA calls, removing the obsolete `pai_t`/`pai.h` abstraction, and moving deferred-work and decay orchestration out of the arena. ([@guangli-dai](https://github.com/guangli-dai): [`1dfa6f7`](https://github.com/jemalloc/jemalloc/commit/1dfa6f7aa45b66f8922ef03c255ee329ee97fb97), [`8edd101`](https://github.com/jemalloc/jemalloc/commit/8edd1012869b3e6d1810001c22198cc148c5d4f2), [`d410f43`](https://github.com/jemalloc/jemalloc/commit/d410f43e1f001e394910a50be9a137dbcbc2eae5)) * Refactor statistics collection and rendering into separate gather/emission stages and descriptor-driven tables. ([@spredolac](https://github.com/spredolac): [`184f304`](https://github.com/jemalloc/jemalloc/commit/184f304dd33ac053a92804ed653fac191bc50377), [`80c8fcb`](https://github.com/jemalloc/jemalloc/commit/80c8fcb4f91119a896479721d1e46e2ad8c9688f)) * Introduce an OS abstraction layer and move platform-dependent file/process I/O, time, synchronization, CPU, virtual-memory, atfork, error-handling, profiling, thread-yield, and configuration-access operations out of allocator core code. ([@guangli-dai](https://github.com/guangli-dai): [`c4158ac`](https://github.com/jemalloc/jemalloc/commit/c4158acac9f45321c38a2222b30b546ed0598737), [`c8e2e01`](https://github.com/jemalloc/jemalloc/commit/c8e2e0134cd13350e33f77515c00e5eb170dc683), ...) Portability improvements: * Replace the `std::__throw_bad_alloc` call with standard C++ ([#2900](https://github.com/jemalloc/jemalloc/pull/2900)). ([@lexprfuncall](https://github.com/lexprfuncall): [`1a15fe3`](https://github.com/jemalloc/jemalloc/commit/1a15fe33a48c52bfe26ea83e49f0d317a47da3ea)) * Make `arena_s` use a flexible array member (`bin_t all_bins[]`) for C99 or newer. ([@grueninger](https://github.com/grueninger): [`300b58b`](https://github.com/jemalloc/jemalloc/commit/300b58b49ba2df0ca524acff8a57a44af170a1c7)) * Fix rdtscp detection with `--with-lg-vaddr`. ([@xinydev](https://github.com/xinydev): [`e8a0d2b`](https://github.com/jemalloc/jemalloc/commit/e8a0d2b477d8da7a087bef98feb7e08d320b8051)) * Fix `malloc_getcpu` on macOS to read the current CPU number correctly. ([@Algunenano](https://github.com/Algunenano): [`5aabbc8`](https://github.com/jemalloc/jemalloc/commit/5aabbc87bf5c6e2e6842f48bd83de41bfa675acc)) * Use `CLOCK_MONOTONIC` for background-thread sleep to prevent clock-rollback stalls, and detect monotonic-condvar support at configure time. ([@antonio2368](https://github.com/antonio2368): [`ebacec3`](https://github.com/jemalloc/jemalloc/commit/ebacec3a1a4ec8b102b9185d897fd8bbde69c313), [`8361239`](https://github.com/jemalloc/jemalloc/commit/8361239b03e9775fd897437d610f249b15fa628a)) * Fix compilation warnings on macOS. ([@gctony](https://github.com/gctony): [`abb0a8a`](https://github.com/jemalloc/jemalloc/commit/abb0a8a05b7d0acb86184cbc0af2a3ce23d74c79)) * Fix thread-exit TSD cleanup on MinGW builds. ([@gctony](https://github.com/gctony): [`1e92317`](https://github.com/jemalloc/jemalloc/commit/1e923170140007c10910376a3c69181e24a993de)) * Fix GCC 16 build warnings by removing `-Wpedantic` violations in macro and function syntax and explicitly NUL-terminating profiling thread-name copies to resolve `-Wstringop-truncation`. ([@grueninger](https://github.com/grueninger): [`5acdcee`](https://github.com/jemalloc/jemalloc/commit/5acdcee60012cb6bbb4d5ecd7f7e2555c88ef404), [`c22d929`](https://github.com/jemalloc/jemalloc/commit/c22d929ab42a4873fcad01e3e044c7247eb04b1e), [@jasonangelov](https://github.com/jasonangelov): [`6a245e0`](https://github.com/jemalloc/jemalloc/commit/6a245e022acddaae5b4164e48855723b943fc032)) * Parse PID-namespace symlinks without glibc-dependent `strtok`/`atol`, and return identifiers as `uint64_t`. ([@guangli-dai](https://github.com/guangli-dai): [`278d90a`](https://github.com/jemalloc/jemalloc/commit/278d90a502aa9601ec5214ad859c050109b13d27)) ### Contributors * [ ](https://github.com/fzakaria) * [ ](https://github.com/Algunenano) * [ ](https://github.com/ibookstein) * [ ](https://github.com/lexprfuncall) * [ ](https://github.com/spredolac) * [ ](https://github.com/bigbruno) * [ ](https://github.com/xinydev) * [ ](https://github.com/binliu19) * [ ](https://github.com/guangli-dai) * [ ](https://github.com/antonio2368) * [ ](https://github.com/grueninger) * [ ](https://github.com/jasonangelov) * [ ](https://github.com/gctony) fzakaria, Algunenano, and 11 other contributors Assets 3 Loading ### Uh oh! There was an error while loading. [Please reload this page](). 10 people reacted 0 [ Join discussion ](/jemalloc/jemalloc/discussions/3005)