Simplify `jemalloc` setup (without perf regression) #148925

madsmtm · 2025-11-13T22:04:52Z

Reland #146627 after fixing the performance regression that caused it to be reverted in #148896.

This avoids 65f0b7a (second commit in the initial PR), and adds a comment explaining why extern crate is needed here instead of use (we need to load tikv_jemalloc_sys from the sysroot for some reason).

r? Kobzol

madsmtm · 2025-11-13T22:05:10Z

I could reproduce the performance regression locally, let's see if rustc-perf agrees:

@bors try
@rust-timer queue

Fix performance regression with jemalloc

rust-bors · 2025-11-14T00:22:43Z

☀️ Try build successful (CI)
Build commit: f30bc23 (f30bc23f4189bac695183835d28078b38cf28d74, parent: 2286e5d224b3413484cf4f398a9f078487e7b49d)

madsmtm · 2025-11-14T01:54:04Z

@bors try
@rust-timer queue

Fix performance regression with jemalloc

rust-bors · 2025-11-14T04:11:24Z

☀️ Try build successful (CI)
Build commit: aef7be6 (aef7be6c425e18433bd4afc8a6ffcccfe9ffe796, parent: 7a72c5459dd58f81b0e1a0e5436d145485889375)

rust-timer · 2025-11-14T05:31:53Z

Finished benchmarking commit (aef7be6): comparison URL.

Overall result: no relevant changes - no action needed

Benchmarking this pull request means it may be perf-sensitive – we'll automatically label it not fit for rolling up. You can override this, but we strongly advise not to, due to possible changes in compiler perf.

@bors rollup=never
@rustbot label: -S-waiting-on-perf -perf-regression

Instruction count

This benchmark run did not return any relevant results for this metric.

Max RSS (memory usage)

Results (primary -0.6%)

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

	mean	range	count
Regressions ❌ (primary)	7.2%	[7.2%, 7.2%]	1
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-8.5%	[-8.5%, -8.5%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-0.6%	[-8.5%, 7.2%]	2

Cycles

Results (secondary 2.2%)

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)	2.2%	[2.2%, 2.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Binary size

This benchmark run did not return any relevant results for this metric.

Bootstrap: 475.201s -> 474.025s (-0.25%)
Artifact size: 388.70 MiB -> 388.66 MiB (-0.01%)

Kobzol

Thanks! This is a great cleanup.

Feel free to r=me once you undraft the PR.

View changes since this review

src/librustdoc/lib.rs

lqd · 2025-11-14T15:11:07Z

src/tools/miri/src/bin/miri.rs

+/// See docs in https://github.com/rust-lang/rust/blob/HEAD/compiler/rustc/src/main.rs
+/// and https://github.com/rust-lang/rust/pull/146627 for why we need this `use` statement.
+#[cfg(any(target_os = "linux", target_os = "macos"))]
+use tikv_jemalloc_sys as _;


would extern crate be needed here too instead of the use?

Nope, miri already uses tikv_jemalloc_sys from Cargo, so extern crate and use work the same here.

Does that mean Miri suffers from the cc-rs issue? The comment in clippy seems to say that the extern crate thing is needed to avoid the cc-rs issue.

madsmtm · 2025-11-15T20:14:11Z

Updated the PR description and title, though I'm gonna wait with merging this until #148957 is done.

@rustbot blocked

rustbot · 2025-11-15T20:14:13Z

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

These commits modify the Cargo.lock file. Unintentional changes to Cargo.lock can be introduced when switching branches and rebasing PRs.

If this was unintentional then you should revert the changes before this PR is merged.
Otherwise, you can ignore this comment.

The Miri subtree was changed

cc @rust-lang/miri

src/librustdoc/lib.rs

Using the new `override_allocator_on_supported_platforms` feature in `tikv-jemalloc-sys v0.6.1` we can avoid the manual statics.

madsmtm added T-rustdoc Relevant to the rustdoc team, which will review and decide on the PR/issue. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Nov 13, 2025

rustbot assigned Kobzol Nov 13, 2025

rustbot added S-waiting-on-author Status: This is awaiting some action (such as code changes or more information) from the author. T-clippy Relevant to the Clippy team. labels Nov 13, 2025