[rluvaton]

jemalloc defines MALLCTL_ARENAS_ALL (jemalloc_macros.h.in) as the arena index that selects all arenas in the arena.<i>.{purge,decay,dss} and stats.arenas.<i>.* mallctls. Its documented use is purging every arena:

mallctl("arena." STRINGIFY(MALLCTL_ARENAS_ALL) ".purge", NULL, NULL, NULL, 0);

Neither crate exposes the constant today, so users hard-code 4096. This PR adds:

• tikv-jemalloc-sys: MALLCTL_ARENAS_ALL: usize = 4096. It is usize to match MIB components and MALLOCX_ARENA(a: usize).
• tikv-jemalloc-ctl:
  • arenas::purge_all() -> Result<()>: builds the MIB for arena.0.purge, sets the arena component to MALLCTL_ARENAS_ALL, and calls mallctlbymib with null old/new pointers. jemalloc's purge ctl requires null pointers and returns EPERM otherwise, which is why this can't go through the existing raw::write.
  • a re-export, arenas::MALLCTL_ARENAS_ALL, so ctl users don't need a direct -sys dependency.
• Build-time check: MALLCTL_ARENAS_ALL is a C macro, so its value has to be hand-written in Rust. It lives in jemalloc-sys/src/macro_consts.rs, which both lib.rs and build.rs include! (the same pattern as src/env.rs). The build script compares it with the #define in the vendored jemalloc_macros.h.in, so a jemalloc update that changes the value fails the build:

  `MALLCTL_ARENAS_ALL` is `4096` in jemalloc/include/jemalloc/jemalloc_macros.h.in but `4095` in src/macro_consts.rs; update src/macro_consts.rs
  

  The check is skipped with JEMALLOC_OVERRIDE, because no headers are available in that case.
• A CHANGELOG entry.

Testing

• New unit test arenas::tests::purge_all_test, plus doctests for purge_all and MALLCTL_ARENAS_ALL.
• cargo test -p tikv-jemalloc-ctl passes with default features and with --no-default-features.
• cargo test -p tikv-jemalloc-sys and cargo fmt --check pass.
• Setting the constant to 4095 makes the build fail with the error above.

Summary by CodeRabbit

• New Features
  • Added an option to purge unused dirty pages across all jemalloc arenas.
  • Made the all-arenas index available for arena-wide control operations.
  • The purge operation reports whether it completed successfully, including errors, so applications can handle failures. Existing per-arena controls remain available.

[ti-chi-bot]

Welcome @rluvaton! It looks like this is your first PR to tikv/jemallocator 🎉

[coderabbitai]

No actionable comments were generated in the recent review.

Walkthrough

The change exposes jemalloc’s all-arenas index and adds arenas::purge_all(). The function uses the index in a purge MIB call. A test checks that the call succeeds after allocating and freeing memory.

Changes: All-Arenas Purge API

Layer / File(s)	Summary
All-arenas index contract jemalloc-sys/src/macro_consts.rs, jemalloc-sys/src/lib.rs, jemalloc-sys/build.rs	The sys crate defines MALLCTL_ARENAS_ALL as 4096, includes the constant, and checks it against the vendored jemalloc header.
Purge all arenas jemalloc-ctl/src/arenas.rs, CHANGELOG.md	The ctl crate re-exports the constant. arenas::purge_all() resolves the arena.0.purge MIB, substitutes the all-arenas index, and calls mallctlbymib. The test allocates and frees 16 MiB before checking for success. The changelog documents the constant and API.

Estimated code review effort: 2 (Simple) | ~10 minutes

Change: Feature

Sequence Diagram(s)

sequenceDiagram
  participant Caller
  participant PurgeAll as arenas::purge_all()
  participant Mallctl as mallctlbymib
  Caller->>PurgeAll: Request purge
  PurgeAll->>PurgeAll: Resolve purge MIB and set MALLCTL_ARENAS_ALL
  PurgeAll->>Mallctl: Call with updated MIB
  Mallctl-->>PurgeAll: Return result
  PurgeAll-->>Caller: Return result

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Possibly related PRs

• tikv/jemallocator#195: Adds the all-arenas index for related mallctl controls, which PR #198 also uses in arenas::purge_all().

Merge Risk: Minimal · up to e3614

No actionable merge risk is established for the all-arenas purge API; it is mergeable after normal checks.

Pre-merge checks: 4 · 1

Failed checks: 1 warning

Check name	Status	Explanation	Resolution
Docstring Coverage		Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documenta…	Write docstrings for the functions missing them to satisfy the coverage threshold.

Passed checks: 4 passed

Check name	Status	Explanation
Description Check		Check skipped - CodeRabbit’s high-level summary is enabled.
Title check		The title clearly and concisely identifies both primary changes: exposing MALLCTL_ARENAS_ALL and adding arenas::purge_all.
Linked Issues check		Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check		Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 66.67% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff with cyclomatic complexity of at least 2. Documentation-only edits and deletions within surviving functions are included; unchanged diff context and fully deleted functions are excluded. Analyzed 3 functions across 4 files. (1 skipped: 1 unsupported.)

Resolution

Write docstrings for the functions missing them to satisfy the coverage threshold.

• Autofix · Keep fixing CodeRabbit findings and required CI, and resolving merge conflicts

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Files selected for processing: 3

• CHANGELOG.md
• jemalloc-ctl/src/arenas.rs
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Files skipped from review as they are similar to previous changes: 3

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• jemalloc-sys/src/macro_consts.rs
• jemalloc-ctl/src/arenas.rs

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Actionable comments posted: 1

---

• Fix comments: Fix CodeRabbit comments on this PR

Prompt to fix all issues

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Inline comments:
Review comments at @jemalloc-ctl/src/arenas.rs:
- Around line 28-29: Update the documentation for MALLCTL_ARENAS_ALL to specify
that it selects `arena.<i>.{initialized,purge,decay,dss}` and
`stats.arenas.<i>.*` keys, rather than all `arena.<i>.*` keys. Apply the same
wording correction in the changelog, preserving the existing re-export note.

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Files selected for processing: 3

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• jemalloc-ctl/src/arenas.rs
• jemalloc-sys/src/lib.rs

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[rluvaton]

Closing in favor of:

• Add a decay_all helper to jemalloc-ctl, triggering arena.4096.decay #195