Replace `jemalloc` bootstrap options with `override-allocator` by Zoxc · Pull Request #155617 · rust-lang/rust

Zoxc · 2026-04-21T20:28:06Z

I want to make use of mimalloc on Windows so this renames jemalloc bootstrap options to override-allocator so we can reuse the same flag for this purpose.

rustbot · 2026-04-21T20:28:09Z

The Miri subtree was changed

cc @rust-lang/miri

Warning

If you are changing how CI LLVM is built or linked, make sure to bump
src/bootstrap/download-ci-llvm-stamp.

cc @jieyouxu

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

This PR modifies src/bootstrap/src/core/config.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

This PR modifies bootstrap.example.toml.

If appropriate, please update CONFIG_CHANGE_HISTORY in src/bootstrap/src/utils/change_tracker.rs.

The rustc-dev-guide subtree was changed. If this PR only touches the dev guide consider submitting a PR directly to rust-lang/rustc-dev-guide otherwise thank you for updating the dev guide with your changes.

cc @BoxyUwU, @tshepang

rustbot · 2026-04-21T20:28:12Z

r? @jieyouxu

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Kobzol · 2026-04-22T19:34:05Z

Just renaming this doesn't make sense on its own; the config and the feature handling would have to be split. override-allocator would take the allocator to use, so it would become a string option, instead of a bool, but then we should still keep the individual features for the different allocators, i.e. jemalloc, mimalloc, etc.

Zoxc · 2026-04-23T00:25:51Z

The idea was to not expose control over which allocator gets used, so you couldn't specify mimalloc on Linux for example. Do we want to support more than one (on a specific target)?

jieyouxu · 2026-04-24T01:22:40Z

@rustbot reroll

Zoxc · 2026-04-29T07:56:05Z

We'll want different approaches on Linux, macOS and Windows to override the C / Rust allocators. Having a single Cargo feature seems like it will result in less cfg! soup than having multiple, but a feature per allocator is possible too.

I'd like some feedback on the direction to take here so I can start working on macOS and Windows PRs on top of this.

Kobzol · 2026-04-29T15:16:51Z

I feel like there are specific things that we want to do per the selected allocator (JEMALLOC_SYS_WITH_LG_PAGE), and also that we will want to repeatedly run benchmarks with jemalloc/mimalloc/etc. on the various OSes, to periodically evaluate their perf. So I'd go towards a feature per allocator. That will also make it easier for us to switch between the allocators on individual OSes more easily.

On the other hand, we will either have to try to build all of the allocators on CI to ensure that they still at least build, or risk that the unused OS/allocator combos might go stale and break.

Kobzol · 2026-07-04T18:36:16Z

We should keep the old jemalloc option for at least half a year for backcompat, as we usually do with breaking config changes.

rustbot · 2026-07-18T11:50:58Z

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

Zoxc · 2026-07-18T11:58:00Z

I added an LLM written commit which adds back the jemalloc option and can be reverted after the grace period.

Kobzol

Left one nit. Please also add a FIXME: remove in Q1 2027 comment on top of the jemalloc field in the bootstrap config.

Otherwise looks good to me.

View changes since this review

Kobzol · 2026-07-21T05:51:14Z

@bors try @rust-timer queue

Replace `jemalloc` bootstrap options with `override-allocator`

rust-bors · 2026-07-21T08:41:10Z

☀️ Try build successful (CI)
Build commit: 22599b1 (22599b18b5e77a2fd4f1d7b71d44319169e8e1a5)
Base parent: 87e5904 (87e5904f5eb6398af6b22eac2802c78934260c48)

rust-timer · 2026-07-21T09:28:07Z

Finished benchmarking commit (22599b1): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking means the PR may be perf-sensitive. Consider adding rollup=never if this change is not fit for rolling up.

@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This perf run didn't have relevant results for this metric.

Max RSS (memory usage)

Results (secondary 3.9%)

A less reliable metric. May be of interest, but not used to determine the overall result above.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	3.9%	[2.5%, 5.2%]	4
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

This perf run didn't have relevant results for this metric.

Binary size

This perf run didn't have relevant results for this metric.

Bootstrap: 486.983s -> 488.14s (0.24%)
Artifact size: 391.82 MiB -> 392.48 MiB (0.17%)

Kobzol · 2026-07-21T09:51:32Z

Perf. looks good, thanks.

@bors r=Mark-Simulacrum,Kobzol

rust-bors · 2026-07-21T09:51:35Z

📌 Commit 011da65 has been approved by Mark-Simulacrum,Kobzol

It is now in the queue for this repository.

…uwer Rollup of 7 pull requests Successful merges: - #155617 (Replace `jemalloc` bootstrap options with `override-allocator`) - #156225 (feat(num): improve error messages for `TryFromIntError`) - #159058 (implement #![feature(macroless_generic_const_args)]) - #159435 (core: implement `Rng` for references) - #159471 (Make `Global` and `System` allocators unstably implement `const Clone + const Default`.) - #159590 (Remove some dead code) - #159636 (Improve some comments (and an error message))

Rollup merge of #155617 - Zoxc:allocator-feature-rename, r=Mark-Simulacrum,Kobzol Replace `jemalloc` bootstrap options with `override-allocator` I want to make [use of `mimalloc` on Windows](#138764) so this renames `jemalloc` bootstrap options to `override-allocator` so we can reuse the same flag for this purpose.

…uwer Rollup of 7 pull requests Successful merges: - rust-lang/rust#155617 (Replace `jemalloc` bootstrap options with `override-allocator`) - rust-lang/rust#156225 (feat(num): improve error messages for `TryFromIntError`) - rust-lang/rust#159058 (implement #![feature(macroless_generic_const_args)]) - rust-lang/rust#159435 (core: implement `Rng` for references) - rust-lang/rust#159471 (Make `Global` and `System` allocators unstably implement `const Clone + const Default`.) - rust-lang/rust#159590 (Remove some dead code) - rust-lang/rust#159636 (Improve some comments (and an error message))

rustbot assigned jieyouxu Apr 21, 2026

Zoxc force-pushed the allocator-feature-rename branch from 0213b60 to 0946ab6 Compare April 21, 2026 20:29

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Zoxc force-pushed the allocator-feature-rename branch from 0946ab6 to fc5ac40 Compare April 21, 2026 20:48

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ada4a reviewed Apr 21, 2026

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Comment thread src/tools/clippy/src/driver.rs Outdated

Zoxc force-pushed the allocator-feature-rename branch from fc5ac40 to 11c97bb Compare April 21, 2026 21:30

tshepang reviewed Apr 22, 2026

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Comment thread src/doc/rustc-dev-guide/src/building/optimized-build.md Outdated

rustbot assigned clubby789 and unassigned jieyouxu Apr 24, 2026

Zoxc force-pushed the allocator-feature-rename branch from 11c97bb to ff48fdf Compare April 30, 2026 08:11

Zoxc changed the title ~~Rename jemalloc bootstrap options to override-allocator~~ Replace jemalloc bootstrap options with override-allocator Apr 30, 2026

Zoxc force-pushed the allocator-feature-rename branch from ff48fdf to 6097bef Compare April 30, 2026 08:13

Replace jemalloc bootstrap options with override-allocator

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Zoxc force-pushed the allocator-feature-rename branch from 6097bef to 23dbc53 Compare July 18, 2026 11:50

rustbot added A-rustc-dev-guide Area: rustc-dev-guide A-testsuite Area: The testsuite used to check the correctness of rustc labels Jul 18, 2026

Kobzol reviewed Jul 20, 2026

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Comment thread src/bootstrap/src/core/config/toml/rust.rs Outdated

Keep jemalloc option for a grace period

011da65

Zoxc force-pushed the allocator-feature-rename branch from 23dbc53 to 011da65 Compare July 20, 2026 20:36

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 21, 2026

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rust-bors Bot pushed a commit that referenced this pull request Jul 21, 2026

Auto merge of #155617 - Zoxc:allocator-feature-rename, r=<try>

22599b1

Replace `jemalloc` bootstrap options with `override-allocator`

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Jul 21, 2026

rust-bors Bot added S-waiting-on-bors Status: Waiting on bors to run and complete tests. Bors will change the label on completion. and removed S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. labels Jul 21, 2026

JonathanBrouwer mentioned this pull request Jul 21, 2026

Rollup of 7 pull requests #159650

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rust-bors Bot merged commit 3c4b83c into rust-lang:main Jul 21, 2026
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rustbot added this to the 1.99.0 milestone Jul 21, 2026

Zoxc deleted the allocator-feature-rename branch July 21, 2026 18:47

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rust-timer commented Jul 21, 2026

Overall result: no relevant changes - no action needed

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