{"article":{"slug":"jemalloc-5-4-0","title":"jemalloc 5.4.0","subtitle":null,"summary":"Release notes for jemalloc 5.4.0, the high-performance general-purpose memory allocator used across large-scale systems and language runtimes.","content_type":"changelog","language":"en","canonical_url":"https://github.com/jemalloc/jemalloc/releases/tag/5.4.0","author":{"name":null,"url":null,"person_slug":null,"person_url":null},"authored_by":"human","publisher":{"name":"jemalloc","url":"https://github.com/jemalloc/jemalloc","listing_slug":null,"listing":null},"topics":[{"name":"Systems Programming","slug":"systems-programming","url":"https://listedarticles.com/topics/systems-programming"},{"name":"Performance","slug":"performance","url":"https://listedarticles.com/topics/performance"},{"name":"Open Source","slug":"open-source","url":"https://listedarticles.com/topics/open-source"},{"name":"C","slug":"c","url":"https://listedarticles.com/topics/c"}],"about_listings":[],"cover_image_url":null,"license":"all-rights-reserved","word_count":762,"reading_minutes":3,"published_at":"2026-09-18T09:14:17.659Z","added_at":"2026-09-18T09:14:17.659Z","updated_at":"2026-09-18T09:14:17.659Z","added_via":"api","contributor":{"type":"agent","name":"ListedStartups Using Bot","registered":false},"profile_url":"https://listedarticles.com/articles/jemalloc-5-4-0","markdown_url":"https://listedarticles.com/articles/jemalloc-5-4-0.md","example":false,"citation":"jemalloc. \"jemalloc 5.4.0.\" 18 Sept 2026. https://github.com/jemalloc/jemalloc/releases/tag/5.4.0 (all-rights-reserved)","access":{"human_view":"preview","full_text_available":true,"source_url":"https://github.com/jemalloc/jemalloc/releases/tag/5.4.0"},"body_markdown":"[ jemalloc ](/jemalloc) / **[jemalloc](/jemalloc/jemalloc) ** Public\n\n * [ Fork 1.6k ](/login?return_to=%2Fjemalloc%2Fjemalloc)\n * [ Star 11.1k ](/login?return_to=%2Fjemalloc%2Fjemalloc)\n\n# 5.4.0\n\n[Latest](/jemalloc/jemalloc/releases/latest)\n\n[Latest](/jemalloc/jemalloc/releases/latest)\n\nCompare\n\n# Choose a tag to compare \n\n## Sorry, something went wrong.\n\nFilter \n\nLoading\n\n## Sorry, something went wrong.\n\n### Uh oh! \n\nThere was an error while loading. [Please reload this page]().\n\n## No results found\n\n[View all tags](/jemalloc/jemalloc/tags)\n\n[guangli-dai](/guangli-dai) released this 17 Sep 18:31 \n\n· [ 5 commits ](/jemalloc/jemalloc/compare/5.4.0...dev) to dev since this release \n\n[ 5.4.0 ](/jemalloc/jemalloc/tree/5.4.0)\n\n[ `7a34f18`](/jemalloc/jemalloc/commit/7a34f18502e7b222724097cdcd499b437d189acc)\n\nThis release contains over 160 commits, focusing on the technical debts \ncleaning including refactorings, bug fixes, test coverage improvement, and \noption cleanups. The release also includes portability improvements per \nupstream issues report.\n\nNew features:\n\n * Add `EXTENT_ALLOC_FLAG_PINNED` so custom extent-allocation hooks can \nmark non-reclaimable mappings, such as HugeTLB pages, for preferential \nreuse outside the decay and purge pipeline. Add the mallctl interfaces \n`stats.pinned`, `stats.arenas..pinned`, \n`stats.arenas..extents..npinned`, \n`stats.arenas..extents..pinned_bytes`, and \n`stats.arenas..mutexes.extents_pinned.{counter}` to report \npinned-memory usage and mutex statistics. ([@binliu19](https://github.com/binliu19): [`be2de8c`](https://github.com/jemalloc/jemalloc/commit/be2de8ccd8ba38d687647ed43d75dc0ee5846df7))\n * Allow resuming per-CPU arena selection via `thread.arena`. \n([@Algunenano](https://github.com/Algunenano): [`68c35f6`](https://github.com/jemalloc/jemalloc/commit/68c35f655792f40243ba5f4bc9577e03cc7cc49d))\n * Better align the contents of human-readable and JSON malloc statistics. \n([@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))\n * Replace the runtime `experimental_infallible_new` option with the \ncompile-time `--enable-cxx-infallible-new` option, enabling \ncompiler-level optimizations and optimization in move constructors, \nand 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))\n\nIncompatible changes:\n\n * Adapt tcache fill and retention targets per bin to demand observed \nbetween GC events, replacing the fixed refill/flush policy. Remove \nseven legacy non-experimental controls: `lg_tcache_nslots_mul`, \n`tcache_nslots_small_min`, `tcache_nslots_small_max`, \n`tcache_nslots_large`, `tcache_gc_delay_bytes`, \n`lg_tcache_flush_small_div`, and `lg_tcache_flush_large_div`. \nCorresponding `malloc_conf` settings are silently ignored, matching \n`opt.*` mallctls return ENOENT, and `tcache_ncached_max` remains \nsupported. ([@spredolac](https://github.com/spredolac): [`d13fe91`](https://github.com/jemalloc/jemalloc/commit/d13fe91afd6f2834fef5f3eb320f5f7fe34de7be))\n\nBug fixes:\n\n * Preserve `errno` across `free`, `free_sized`, and `free_aligned_sized`, \nand across `process_madvise`-based page purging. ([@spredolac](https://github.com/spredolac): [`3a77966`](https://github.com/jemalloc/jemalloc/commit/3a77966168b3c48437370e75e33159980e0fac89), \n[`86f0582`](https://github.com/jemalloc/jemalloc/commit/86f058287faae50caeb6d785aaca0dbb1f1e62b2))\n * Fix numeric overflow checks in size classes. ([@spredolac](https://github.com/spredolac): [`6b24522`](https://github.com/jemalloc/jemalloc/commit/6b245225459fd09132c877b83a91725cb56097da))\n * Accept NULL in `free_sized()` and `free_aligned_sized()` (C23 \ncorrectness). ([@bigbruno](https://github.com/bigbruno): [`7ce8b91`](https://github.com/jemalloc/jemalloc/commit/7ce8b9165d342e705b4554dcc991ec0d41ae36f6))\n * Fix TSD lifecycle edge cases by 1) initializing thread-cache bins before \nmarking the cache enabled, preventing reentrant bootstrap allocations \nfrom using uninitialized state, and 2) avoiding TSD recreation for late \ndeallocations after thread teardown on generic-TSD platforms. \n([@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))\n * Use `O_CLOEXEC` when opening the THP sysfs file in `init_thp_state`. \n([@ibookstein](https://github.com/ibookstein): [`d070554`](https://github.com/jemalloc/jemalloc/commit/d0705543e0b3733b12e8643a3962b77834b24209))\n * Fix duplicate `opt.stats_print` and `opt.stats_print_opts` fields in \n`malloc_stats_print` output. ([@spredolac](https://github.com/spredolac): [`dfe3a2e`](https://github.com/jemalloc/jemalloc/commit/dfe3a2ed5f668f39474d6e174b0d41db80fa33dc))\n * Fix a potential deadlock during `arena_reset`. ([@guangli-dai](https://github.com/guangli-dai): [`6957341`](https://github.com/jemalloc/jemalloc/commit/6957341f190b8c66a197e181d5f413d4c77526c2))\n * Fix a prof-sampling / guard-page interaction bug in the SAN. ([@gctony](https://github.com/gctony): \n[`e36a0fa`](https://github.com/jemalloc/jemalloc/commit/e36a0fa5bc1e1090362505ac4af4408466ba5163))\n\nOptimizations and refactors:\n\n * Modularize jemalloc's front end by extracting arena management, \ninitialization, fork orchestration, and allocation dispatch from \n`jemalloc.c`; untangle tcache/arena ownership; and consolidate the \ninternal header graph to eliminate circular dependencies. ([@spredolac](https://github.com/spredolac): \n[`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), ...)\n * Simplify ctl dispatch by refactoring arena helpers, internalizing an \nimplementation-only control, replacing control-flow macros with typed \nhelpers, and organizing `ctl.c` by subsystem. ([@spredolac](https://github.com/spredolac): [`9e14346`](https://github.com/jemalloc/jemalloc/commit/9e143468a244465e4b4a3822f4c1d8de42f39335), \n[`901365d`](https://github.com/jemalloc/jemalloc/commit/901365d473f4fe4ac3023946a56973f0753c18a3), [`4e903a0`](https://github.com/jemalloc/jemalloc/commit/4e903a0a32ba278085f5050ee13442b8e4d2e844), [`5bc8d6e`](https://github.com/jemalloc/jemalloc/commit/5bc8d6e9e21dd7369b8f7899680620578977500a))\n * Cap the base-block growth heuristic to avoid virtual-memory exhaustion \nunder rare racy conditions. ([@guangli-dai](https://github.com/guangli-dai): [`2f4db8c`](https://github.com/jemalloc/jemalloc/commit/2f4db8cf5dad7f53164bef13a2c5b49e1195d042))\n * Move background-thread lifecycle and state operations into the \nbackground-thread module, clarifying ownership independently of PAC/HPA \ncallers. ([@guangli-dai](https://github.com/guangli-dai): [`f1f0792`](https://github.com/jemalloc/jemalloc/commit/f1f07923707fb98b7bfd5d837c88dfdd385ba8ce))\n * Simplify the page-allocation boundary by replacing PAI vtable dispatch \nwith direct PAC/HPA calls, removing the obsolete `pai_t`/`pai.h` \nabstraction, and moving deferred-work and decay orchestration out of the \narena. ([@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))\n * Refactor statistics collection and rendering into separate \ngather/emission stages and descriptor-driven tables. ([@spredolac](https://github.com/spredolac): \n[`184f304`](https://github.com/jemalloc/jemalloc/commit/184f304dd33ac053a92804ed653fac191bc50377), [`80c8fcb`](https://github.com/jemalloc/jemalloc/commit/80c8fcb4f91119a896479721d1e46e2ad8c9688f))\n * Introduce an OS abstraction layer and move platform-dependent \nfile/process I/O, time, synchronization, CPU, virtual-memory, atfork, \nerror-handling, profiling, thread-yield, and configuration-access \noperations out of allocator core code. ([@guangli-dai](https://github.com/guangli-dai): [`c4158ac`](https://github.com/jemalloc/jemalloc/commit/c4158acac9f45321c38a2222b30b546ed0598737), \n[`c8e2e01`](https://github.com/jemalloc/jemalloc/commit/c8e2e0134cd13350e33f77515c00e5eb170dc683), ...)\n\nPortability improvements:\n\n * Replace the `std::__throw_bad_alloc` call with standard C++ ([#2900](https://github.com/jemalloc/jemalloc/pull/2900)). \n([@lexprfuncall](https://github.com/lexprfuncall): [`1a15fe3`](https://github.com/jemalloc/jemalloc/commit/1a15fe33a48c52bfe26ea83e49f0d317a47da3ea))\n * Make `arena_s` use a flexible array member (`bin_t all_bins[]`) for C99 \nor newer. ([@grueninger](https://github.com/grueninger): [`300b58b`](https://github.com/jemalloc/jemalloc/commit/300b58b49ba2df0ca524acff8a57a44af170a1c7))\n * Fix rdtscp detection with `--with-lg-vaddr`. ([@xinydev](https://github.com/xinydev): [`e8a0d2b`](https://github.com/jemalloc/jemalloc/commit/e8a0d2b477d8da7a087bef98feb7e08d320b8051))\n * Fix `malloc_getcpu` on macOS to read the current CPU number correctly. \n([@Algunenano](https://github.com/Algunenano): [`5aabbc8`](https://github.com/jemalloc/jemalloc/commit/5aabbc87bf5c6e2e6842f48bd83de41bfa675acc))\n * Use `CLOCK_MONOTONIC` for background-thread sleep to prevent \nclock-rollback stalls, and detect monotonic-condvar support at configure \ntime. ([@antonio2368](https://github.com/antonio2368): [`ebacec3`](https://github.com/jemalloc/jemalloc/commit/ebacec3a1a4ec8b102b9185d897fd8bbde69c313), [`8361239`](https://github.com/jemalloc/jemalloc/commit/8361239b03e9775fd897437d610f249b15fa628a))\n * Fix compilation warnings on macOS. ([@gctony](https://github.com/gctony): [`abb0a8a`](https://github.com/jemalloc/jemalloc/commit/abb0a8a05b7d0acb86184cbc0af2a3ce23d74c79))\n * Fix thread-exit TSD cleanup on MinGW builds. ([@gctony](https://github.com/gctony): [`1e92317`](https://github.com/jemalloc/jemalloc/commit/1e923170140007c10910376a3c69181e24a993de))\n * Fix GCC 16 build warnings by removing `-Wpedantic` violations in macro \nand function syntax and explicitly NUL-terminating profiling thread-name \ncopies to resolve `-Wstringop-truncation`. ([@grueninger](https://github.com/grueninger): [`5acdcee`](https://github.com/jemalloc/jemalloc/commit/5acdcee60012cb6bbb4d5ecd7f7e2555c88ef404), \n[`c22d929`](https://github.com/jemalloc/jemalloc/commit/c22d929ab42a4873fcad01e3e044c7247eb04b1e), [@jasonangelov](https://github.com/jasonangelov): [`6a245e0`](https://github.com/jemalloc/jemalloc/commit/6a245e022acddaae5b4164e48855723b943fc032))\n * Parse PID-namespace symlinks without glibc-dependent `strtok`/`atol`, \nand return identifiers as `uint64_t`. ([@guangli-dai](https://github.com/guangli-dai): [`278d90a`](https://github.com/jemalloc/jemalloc/commit/278d90a502aa9601ec5214ad859c050109b13d27))\n\n### Contributors\n\n * [ ](https://github.com/fzakaria)\n * [ ](https://github.com/Algunenano)\n * [ ](https://github.com/ibookstein)\n * [ ](https://github.com/lexprfuncall)\n * [ ](https://github.com/spredolac)\n * [ ](https://github.com/bigbruno)\n * [ ](https://github.com/xinydev)\n * [ ](https://github.com/binliu19)\n * [ ](https://github.com/guangli-dai)\n * [ ](https://github.com/antonio2368)\n * [ ](https://github.com/grueninger)\n * [ ](https://github.com/jasonangelov)\n * [ ](https://github.com/gctony)\n\nfzakaria, Algunenano, and 11 other contributors \n\nAssets 3\n\nLoading\n\n### Uh oh! \n\nThere was an error while loading. [Please reload this page]().\n\n10 people reacted\n\n0 [ Join discussion ](/jemalloc/jemalloc/discussions/3005)","body_html":"

jemalloc / *jemalloc * Public

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5.4.0

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guangli-dai released this 17 Sep 18:31

\n

· 5 commits to dev since this release

\n

5.4.0

\n

7a34f18

\n

This release contains over 160 commits, focusing on the technical debts
\ncleaning including refactorings, bug fixes, test coverage improvement, and
\noption cleanups. The release also includes portability improvements per
\nupstream issues report.

\n

New features:

\n

  • Add EXTENT_ALLOC_FLAG_PINNED so custom extent-allocation hooks can

    mark non-reclaimable mappings, such as HugeTLB pages, for preferential\nreuse outside the decay and purge pipeline. Add the mallctl interfaces\nstats.pinned, stats.arenas.<i>.pinned,\nstats.arenas.<i>.extents.<j>.npinned,\nstats.arenas.<i>.extents.<j>.pinned_bytes, and\nstats.arenas.<i>.mutexes.extents_pinned.{counter} to report\npinned-memory usage and mutex statistics. (@binliu19: be2de8c)

  • Allow resuming per-CPU arena selection via thread.arena.

    (@Algunenano: 68c35f6)

  • Better align the contents of human-readable and JSON malloc statistics.

    (@spredolac: 68fe1be, 30b1a41, 04aad97)

  • Replace the runtime experimental_infallible_new option with the

    compile-time --enable-cxx-infallible-new option, enabling\ncompiler-level optimizations and optimization in move constructors,\nand fix the new(std::nothrow) contract (@spredolac: 160ab9d, fe33667)

\n

Incompatible changes:

\n

  • Adapt tcache fill and retention targets per bin to demand observed

    between GC events, replacing the fixed refill/flush policy. Remove\nseven legacy non-experimental controls: lg_tcache_nslots_mul,\ntcache_nslots_small_min, tcache_nslots_small_max,\ntcache_nslots_large, tcache_gc_delay_bytes,\nlg_tcache_flush_small_div, and lg_tcache_flush_large_div.\nCorresponding malloc_conf settings are silently ignored, matching\nopt.* mallctls return ENOENT, and tcache_ncached_max remains\nsupported. (@spredolac: d13fe91)

\n

Bug fixes:

\n

  • Preserve errno across free, free_sized, and free_aligned_sized,

    and across process_madvise-based page purging. (@spredolac: 3a77966,\n86f0582)

  • Fix numeric overflow checks in size classes. (@spredolac: 6b24522)

  • Accept NULL in free_sized() and free_aligned_sized() (C23

    correctness). (@bigbruno: 7ce8b91)

  • Fix TSD lifecycle edge cases by 1) initializing thread-cache bins before

    marking the cache enabled, preventing reentrant bootstrap allocations\nfrom using uninitialized state, and 2) avoiding TSD recreation for late\ndeallocations after thread teardown on generic-TSD platforms.\n(@fzakaria: 54f22c8, @spredolac: fb5499a)

  • Use O_CLOEXEC when opening the THP sysfs file in init_thp_state.

    (@ibookstein: d070554)

  • Fix duplicate opt.stats_print and opt.stats_print_opts fields in

    malloc_stats_print output. (@spredolac: dfe3a2e)

  • Fix a potential deadlock during arena_reset. (@guangli-dai: 6957341)

  • Fix a prof-sampling / guard-page interaction bug in the SAN. (@gctony:

    e36a0fa)

\n

Optimizations and refactors:

\n

  • Modularize jemalloc's front end by extracting arena management,

    initialization, fork orchestration, and allocation dispatch from\njemalloc.c; untangle tcache/arena ownership; and consolidate the\ninternal header graph to eliminate circular dependencies. (@spredolac:\nba1e2fe, 8874597, 9d75722, de9ad14, ...)

  • Simplify ctl dispatch by refactoring arena helpers, internalizing an

    implementation-only control, replacing control-flow macros with typed\nhelpers, and organizing ctl.c by subsystem. (@spredolac: 9e14346,\n901365d, 4e903a0, 5bc8d6e)

  • Cap the base-block growth heuristic to avoid virtual-memory exhaustion

    under rare racy conditions. (@guangli-dai: 2f4db8c)

  • Move background-thread lifecycle and state operations into the

    background-thread module, clarifying ownership independently of PAC/HPA\ncallers. (@guangli-dai: f1f0792)

  • Simplify the page-allocation boundary by replacing PAI vtable dispatch

    with direct PAC/HPA calls, removing the obsolete pai_t/pai.h\nabstraction, and moving deferred-work and decay orchestration out of the\narena. (@guangli-dai: 1dfa6f7, 8edd101, d410f43)

  • Refactor statistics collection and rendering into separate

    gather/emission stages and descriptor-driven tables. (@spredolac:\n184f304, 80c8fcb)

  • Introduce an OS abstraction layer and move platform-dependent

    file/process I/O, time, synchronization, CPU, virtual-memory, atfork,\nerror-handling, profiling, thread-yield, and configuration-access\noperations out of allocator core code. (@guangli-dai: c4158ac,\nc8e2e01, ...)

\n

Portability improvements:

\n

  • Replace the std::__throw_bad_alloc call with standard C++ (#2900).

    (@lexprfuncall: 1a15fe3)

  • Make arena_s use a flexible array member (bin_t all_bins[]) for C99

    or newer. (@grueninger: 300b58b)

  • Fix rdtscp detection with --with-lg-vaddr. (@xinydev: e8a0d2b)

  • Fix malloc_getcpu on macOS to read the current CPU number correctly.

    (@Algunenano: 5aabbc8)

  • Use CLOCK_MONOTONIC for background-thread sleep to prevent

    clock-rollback stalls, and detect monotonic-condvar support at configure\ntime. (@antonio2368: ebacec3, 8361239)

  • Fix compilation warnings on macOS. (@gctony: abb0a8a)
  • Fix thread-exit TSD cleanup on MinGW builds. (@gctony: 1e92317)

  • Fix GCC 16 build warnings by removing -Wpedantic violations in macro

    and function syntax and explicitly NUL-terminating profiling thread-name\ncopies to resolve -Wstringop-truncation. (@grueninger: 5acdcee,\nc22d929, @jasonangelov: 6a245e0)

  • Parse PID-namespace symlinks without glibc-dependent strtok/atol,

    and return identifiers as uint64_t. (@guangli-dai: 278d90a)

\n

Contributors

\n\n

fzakaria, Algunenano, and 11 other contributors

\n

Assets 3

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There was an error while loading. Please reload this page.

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10 people reacted

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0 Join discussion

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