Garbage-collect old incremental compilation sessions by charliermarsh · Pull Request #162240 · rust-lang/rust

charliermarsh · 2026-09-03T13:12:33Z

Summary

rustc cleans up old incremental-cache snapshots twice during a compilation: once at startup (after loading the previous cache), and then again after finishing and finalizing the new cache.

In #147821, we started skipping the current session during cleanup. But that means we're also skipping cleanup after the session has finished, so we're keeping both the previous and the completed snapshot on disk. (The snapshots don't accumulate indefinitely -- the "extra" snapshot gets removed when the next compilation starts, but that compilation then leaves another snapshot behind when it finishes.)

This PR modifies the logic to skip the current session while it is still active, but remove it once finalized.

Testing it locally for Ruff and uv, the target directory shrinks significantly... The query caches are almost exactly 50% smaller, and target as a whole is 27.3% smaller in Ruff and 31.1% smaller in uv.

rustbot · 2026-09-03T13:12:41Z

r? @TaKO8Ki

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lqd · 2026-09-03T15:37:05Z

@bors try @rust-timer queue

… r=<try> Garbage-collect old incremental compilation sessions

rust-bors · 2026-09-03T16:36:43Z

☀️ Try build successful (CI)
Build commit: 0cc728b (0cc728b666accd70541869cd29761c27af2a1bda)
Base parent: d8df826 (d8df82673d5911b6112a85bf91d9adefb2c66a1a)

rust-timer · 2026-09-03T17:19:37Z

Finished benchmarking commit (0cc728b): comparison URL.

Overall result: ✅ improvements - 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

Our most reliable metric. Used to determine the overall result above. However, even this metric can be noisy.

	mean	range	count
Regressions ❌ (primary)	-	-	0
Regressions ❌ (secondary)	-	-	0
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	-	-	0

Max RSS (memory usage)

Results (secondary 7.2%)

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)	7.2%	[7.2%, 7.2%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-	-	0

Cycles

Results (secondary -2.6%)

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)	2.7%	[2.7%, 2.7%]	1
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-5.2%	[-6.2%, -4.2%]	2
All ❌✅ (primary)	-	-	0

Binary size

Results (primary 0.0%, secondary 0.1%)

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

	mean	range	count
Regressions ❌ (primary)	0.0%	[0.0%, 0.1%]	15
Regressions ❌ (secondary)	0.1%	[0.0%, 0.1%]	5
Improvements ✅ (primary)	-	-	0
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	0.0%	[0.0%, 0.1%]	15

Bootstrap: 477.112s -> 477.159s (0.01%)
Artifact size: 401.86 MiB -> 401.22 MiB (-0.16%)

lqd · 2026-09-03T17:25:56Z

It’s the previous behavior isn’t intended, so this fix would make sense. What do you think @bjorn3?

bjorn3 · 2026-09-14T09:07:00Z

@bors r+

rust-bors · 2026-09-14T09:07:04Z

📌 Commit b4361c9 has been approved by bjorn3

It is now in the queue for this repository.

bjorn3 · 2026-09-14T09:07:17Z

r? bjorn3

…session-gc, r=bjorn3 Garbage-collect old incremental compilation sessions ## Summary rustc cleans up old incremental-cache snapshots twice during a compilation: once at startup (after loading the previous cache), and then again after finishing and finalizing the new cache. In rust-lang#147821, we started skipping the current session during cleanup. But that means we're also skipping cleanup _after_ the session has finished, so we're keeping _both_ the previous and the completed snapshot on disk. (The snapshots don't accumulate indefinitely -- the "extra" snapshot gets removed when the next compilation starts, but that compilation then leaves another snapshot behind when it finishes.) This PR modifies the logic to skip the current session while it is still active, but remove it once finalized. Testing it locally for [Ruff](https://github.com/astral-sh/ruff) and [uv](https://github.com/astral-sh/uv), the target directory shrinks significantly... The query caches are almost exactly 50% smaller, and `target` as a whole is 27.3% smaller in Ruff and 31.1% smaller in uv.

…uwer Rollup of 11 pull requests Successful merges: - #162752 (`rust-analyzer` subtree update) - #161868 (libtest: never iterate over all tests in `--exact` mode) - #161903 (Fix initialization cycle in `target_config`) - #162240 (Garbage-collect old incremental compilation sessions) - #161675 (document that t-lang does not need involvement for unobservable intrisics) - #162630 (Simplify the `G` in `Diag<'a, G>`) - #162647 (Add regression test for previous overflow evaluating the requirement) - #162703 (regression test for valtree leaf const) - #162723 (Add regression test for unexpected type for constructor) - #162735 (Remove pointless `A: Allocator` bounds in boxed.rs) - #162736 (clean up trivial region constraint filtering)

…session-gc, r=bjorn3 Garbage-collect old incremental compilation sessions ## Summary rustc cleans up old incremental-cache snapshots twice during a compilation: once at startup (after loading the previous cache), and then again after finishing and finalizing the new cache. In rust-lang#147821, we started skipping the current session during cleanup. But that means we're also skipping cleanup _after_ the session has finished, so we're keeping _both_ the previous and the completed snapshot on disk. (The snapshots don't accumulate indefinitely -- the "extra" snapshot gets removed when the next compilation starts, but that compilation then leaves another snapshot behind when it finishes.) This PR modifies the logic to skip the current session while it is still active, but remove it once finalized. Testing it locally for [Ruff](https://github.com/astral-sh/ruff) and [uv](https://github.com/astral-sh/uv), the target directory shrinks significantly... The query caches are almost exactly 50% smaller, and `target` as a whole is 27.3% smaller in Ruff and 31.1% smaller in uv.

…uwer Rollup of 15 pull requests Successful merges: - #162752 (`rust-analyzer` subtree update) - #161903 (Fix initialization cycle in `target_config`) - #162240 (Garbage-collect old incremental compilation sessions) - #162610 (fix tailcall indirect return) - #162634 (Implement semantic analysis for named `Fn` trait params) - #161675 (document that t-lang does not need involvement for unobservable intrisics) - #162160 (turn aligned-in-packed error into lint) - #162504 (Stabilize `unsafe_cell_access`) - #162516 (tidy: Sort multi-line types by treating `>` as a closing bracket) - #162630 (Simplify the `G` in `Diag<'a, G>`) - #162647 (Add regression test for previous overflow evaluating the requirement) - #162703 (regression test for valtree leaf const) - #162723 (Add regression test for unexpected type for constructor) - #162735 (Remove pointless `A: Allocator` bounds in boxed.rs) - #162736 (clean up trivial region constraint filtering)

…uwer Rollup of 16 pull requests Successful merges: - #162762 (Subtree sync for rustc_codegen_cranelift) - #162752 (`rust-analyzer` subtree update) - #161903 (Fix initialization cycle in `target_config`) - #162240 (Garbage-collect old incremental compilation sessions) - #162610 (fix tailcall indirect return) - #162634 (Implement semantic analysis for named `Fn` trait params) - #161675 (document that t-lang does not need involvement for unobservable intrisics) - #162160 (turn aligned-in-packed error into lint) - #162504 (Stabilize `unsafe_cell_access`) - #162516 (tidy: Sort multi-line types by treating `>` as a closing bracket) - #162630 (Simplify the `G` in `Diag<'a, G>`) - #162647 (Add regression test for previous overflow evaluating the requirement) - #162703 (regression test for valtree leaf const) - #162723 (Add regression test for unexpected type for constructor) - #162735 (Remove pointless `A: Allocator` bounds in boxed.rs) - #162736 (clean up trivial region constraint filtering)

Rollup merge of #162240 - charliermarsh:charlie/incremental-session-gc, r=bjorn3 Garbage-collect old incremental compilation sessions ## Summary rustc cleans up old incremental-cache snapshots twice during a compilation: once at startup (after loading the previous cache), and then again after finishing and finalizing the new cache. In #147821, we started skipping the current session during cleanup. But that means we're also skipping cleanup _after_ the session has finished, so we're keeping _both_ the previous and the completed snapshot on disk. (The snapshots don't accumulate indefinitely -- the "extra" snapshot gets removed when the next compilation starts, but that compilation then leaves another snapshot behind when it finishes.) This PR modifies the logic to skip the current session while it is still active, but remove it once finalized. Testing it locally for [Ruff](https://github.com/astral-sh/ruff) and [uv](https://github.com/astral-sh/uv), the target directory shrinks significantly... The query caches are almost exactly 50% smaller, and `target` as a whole is 27.3% smaller in Ruff and 31.1% smaller in uv.

…uwer Rollup of 16 pull requests Successful merges: - rust-lang/rust#162762 (Subtree sync for rustc_codegen_cranelift) - rust-lang/rust#162752 (`rust-analyzer` subtree update) - rust-lang/rust#161903 (Fix initialization cycle in `target_config`) - rust-lang/rust#162240 (Garbage-collect old incremental compilation sessions) - rust-lang/rust#162610 (fix tailcall indirect return) - rust-lang/rust#162634 (Implement semantic analysis for named `Fn` trait params) - rust-lang/rust#161675 (document that t-lang does not need involvement for unobservable intrisics) - rust-lang/rust#162160 (turn aligned-in-packed error into lint) - rust-lang/rust#162504 (Stabilize `unsafe_cell_access`) - rust-lang/rust#162516 (tidy: Sort multi-line types by treating `>` as a closing bracket) - rust-lang/rust#162630 (Simplify the `G` in `Diag<'a, G>`) - rust-lang/rust#162647 (Add regression test for previous overflow evaluating the requirement) - rust-lang/rust#162703 (regression test for valtree leaf const) - rust-lang/rust#162723 (Add regression test for unexpected type for constructor) - rust-lang/rust#162735 (Remove pointless `A: Allocator` bounds in boxed.rs) - rust-lang/rust#162736 (clean up trivial region constraint filtering)

rustbot assigned TaKO8Ki Sep 3, 2026

rustbot added A-run-make Area: port run-make Makefiles to rmake.rs S-waiting-on-review Status: Awaiting review from the assignee but also interested parties. T-compiler Relevant to the compiler team, which will review and decide on the PR/issue. labels Sep 3, 2026

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charliermarsh changed the title ~~Collect superseded incremental compilation sessions~~ Garbage-collect superseded incremental compilation sessions Sep 3, 2026

charliermarsh force-pushed the charlie/incremental-session-gc branch from d7c7cb1 to 62352f9 Compare September 3, 2026 13:14

charliermarsh changed the title ~~Garbage-collect superseded incremental compilation sessions~~ Garbage-collect old incremental compilation sessions Sep 3, 2026

Garbage-collect old incremental compilation sessions

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charliermarsh force-pushed the charlie/incremental-session-gc branch from 62352f9 to bc21abb Compare September 3, 2026 13:15

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rustbot added the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 3, 2026

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rust-bors Bot pushed a commit that referenced this pull request Sep 3, 2026

Auto merge of #162240 - charliermarsh:charlie/incremental-session-gc,…

0cc728b

… r=<try> Garbage-collect old incremental compilation sessions

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rustbot removed the S-waiting-on-perf Status: Waiting on a perf run to be completed. label Sep 3, 2026

bjorn3 reviewed Sep 3, 2026

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charliermarsh added 2 commits September 4, 2026 12:34

Preserve the current finalized incremental session

f178bea

Move guard into is_old_enough_to_be_collected branch

b4361c9

charliermarsh requested a review from bjorn3 September 11, 2026 16:56

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-review Status: Awaiting review from the assignee but also interested parties. labels Sep 14, 2026

rustbot assigned bjorn3 and unassigned TaKO8Ki Sep 14, 2026

JonathanBrouwer mentioned this pull request Sep 14, 2026

Rollup of 11 pull requests #162755

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JonathanBrouwer mentioned this pull request Sep 14, 2026

Rollup of 15 pull requests #162764

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JonathanBrouwer mentioned this pull request Sep 14, 2026

Rollup of 16 pull requests #162767

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rust-bors Bot merged commit f654635 into rust-lang:main Sep 14, 2026
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rustbot added this to the 1.100.0 milestone Sep 14, 2026

dpotapov mentioned this pull request Sep 15, 2026

chore: pin Rust to nightly-2026-09-15 admte/orc#1

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asopitech mentioned this pull request Sep 18, 2026

[Experiment] Rust IRを状態として持ち続けることは実現可能か — 持続可能性と省エネ性の検証(レイアウト最適化の前段) asopitech-labs/laminaria-rust-nim-toolchain#67

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bjorn3 added the A-incr-comp Area: Incremental compilation label Sep 18, 2026

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Garbage-collect old incremental compilation sessions - #162240

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Overall result: ✅ improvements - no action needed

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