Shrink `PartialRes` and its alignment by joshtriplett · Pull Request #163916 · rust-lang/rust

joshtriplett · 2026-10-07T03:36:19Z

A couple of places store NodeMap<PartialRes>, which is FxHashMap<NodeId, PartialRes>, which stores (NodeId, PartialRes).

(NodeId, PartialRes) takes up 32 bytes. PartialRes contains a usize count of unresolved segments, in that path. We don't need room for more than 2^32 unresolved segments, so store it as a u32. That shrinks PartialRes and reduces its alignment, so (NodeId, PartialRes) shrinks to 20 bytes.

We store a lot of those.

For aws-sdk-ec2 (full check), this reduces max-rss by ~102 MiB (1.84%)

A couple of places store `NodeMap<PartialRes>`, which is `FxHashMap<NodeId, PartialRes>`, which stores `(NodeId, PartialRes)`. `(NodeId, PartialRes)` takes up 32 bytes. `PartialRes` contains a `usize` count of unresolved segments, in *that* path. We don't need room for more than 2^32 unresolved segments, so store it as a u32. That shrinks `PartialRes` and reduces its alignment, so `(NodeId, PartialRes)` shrinks to 20 bytes. We store a *lot* of those. For aws-sdk-ec2 (full check), this reduces max-rss by ~102 MiB (1.84%)

rustbot · 2026-10-07T03:36:24Z

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joshtriplett · 2026-10-07T03:36:42Z

@bors try @rust-timer queue

Shrink `PartialRes` and its alignment

rust-bors · 2026-10-07T04:36:43Z

☀️ Try build successful (CI)
Build commit: 7035dc6 (7035dc6ae3d9b54364207d000754dc089c409cb7)
Base parent: 8d1a764 (8d1a76430406c877b35d0b627e7f796dcf0dfeca)

rust-timer · 2026-10-07T06:09:13Z

Finished benchmarking commit (7035dc6): 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)	-0.8%	[-0.9%, -0.7%]	2
Improvements ✅ (secondary)	-0.1%	[-0.1%, -0.1%]	1
All ❌✅ (primary)	-0.8%	[-0.9%, -0.7%]	2

Max RSS (memory usage)

Results (primary -0.8%, 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)	1.9%	[0.6%, 2.7%]	10
Regressions ❌ (secondary)	1.9%	[1.0%, 3.0%]	9
Improvements ✅ (primary)	-1.6%	[-3.2%, -0.5%]	31
Improvements ✅ (secondary)	-1.9%	[-5.9%, -0.6%]	8
All ❌✅ (primary)	-0.8%	[-3.2%, 2.7%]	41

Cycles

Results (primary -2.3%)

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)	-	-	0
Improvements ✅ (primary)	-2.3%	[-2.3%, -2.3%]	1
Improvements ✅ (secondary)	-	-	0
All ❌✅ (primary)	-2.3%	[-2.3%, -2.3%]	1

Binary size

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

Bootstrap: 489.893s -> 489.532s (-0.07%)
Artifact size: 408.60 MiB -> 408.63 MiB (0.01%)

lqd · 2026-10-07T06:14:43Z

Nice!

r? me @bors r+

rust-bors · 2026-10-07T06:14:47Z

📌 Commit aaa57c9 has been approved by lqd

It is now in the queue for this repository.

Shrink `PartialRes` and its alignment A couple of places store `NodeMap<PartialRes>`, which is `FxHashMap<NodeId, PartialRes>`, which stores `(NodeId, PartialRes)`. `(NodeId, PartialRes)` takes up 32 bytes. `PartialRes` contains a `usize` count of unresolved segments, in *that* path. We don't need room for more than 2^32 unresolved segments, so store it as a u32. That shrinks `PartialRes` and reduces its alignment, so `(NodeId, PartialRes)` shrinks to 20 bytes. We store a *lot* of those. For aws-sdk-ec2 (full check), this reduces max-rss by ~102 MiB (1.84%)

…uwer Rollup of 25 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #162156 (add IBM f128 type) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163257 (abby DSL: sanity checks on forall where clauses) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

Shrink `PartialRes` and its alignment A couple of places store `NodeMap<PartialRes>`, which is `FxHashMap<NodeId, PartialRes>`, which stores `(NodeId, PartialRes)`. `(NodeId, PartialRes)` takes up 32 bytes. `PartialRes` contains a `usize` count of unresolved segments, in *that* path. We don't need room for more than 2^32 unresolved segments, so store it as a u32. That shrinks `PartialRes` and reduces its alignment, so `(NodeId, PartialRes)` shrinks to 20 bytes. We store a *lot* of those. For aws-sdk-ec2 (full check), this reduces max-rss by ~102 MiB (1.84%)

…uwer Rollup of 24 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163257 (abby DSL: sanity checks on forall where clauses) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

…uwer Rollup of 23 pull requests Successful merges: - #163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - #163806 (even more `tests/crashes` migration for `-Znext-solver`) - #163508 (Document the `rustc_on_unimplemented` attribute.) - #163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - #163863 (use the type name instead of `Self` in constructor paths again) - #163864 (Remove CLAUDE.md) - #163877 (Add regression test for duplicated rustdoc search results between std and core) - #163916 (Shrink `PartialRes` and its alignment) - #149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - #152557 (Oneshot `is_ready`) - #157273 (Stabilize `optimize` attribute) - #162000 (peel_transparent_wrappers only works on non-1ZST) - #163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - #163348 (perf:cache FFI safety results in improper_ctypes lint) - #163768 (Move more `rustdoc-html` tests in the right location) - #163778 (check is_indirect_first_projection when replacing in RefProp) - #163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - #163807 (Add `has_reliable_f16b` for Arm) - #163809 (Switch TLS implementation for wasi and bump SDK version to 34) - #163826 (Update books) - #163849 (ci: update to PowerShell 7.6.6) - #163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - #163870 (Add if-installed:auto:spellcheck to pre-push script)

Rollup merge of #163916 - joshtriplett:partialres-shrink, r=lqd Shrink `PartialRes` and its alignment A couple of places store `NodeMap<PartialRes>`, which is `FxHashMap<NodeId, PartialRes>`, which stores `(NodeId, PartialRes)`. `(NodeId, PartialRes)` takes up 32 bytes. `PartialRes` contains a `usize` count of unresolved segments, in *that* path. We don't need room for more than 2^32 unresolved segments, so store it as a u32. That shrinks `PartialRes` and reduces its alignment, so `(NodeId, PartialRes)` shrinks to 20 bytes. We store a *lot* of those. For aws-sdk-ec2 (full check), this reduces max-rss by ~102 MiB (1.84%)

…uwer Rollup of 23 pull requests Successful merges: - rust-lang/rust#163090 (Run LLDB debuginfo tests on `x86_64-pc-windows-msvc` in CI) - rust-lang/rust#163806 (even more `tests/crashes` migration for `-Znext-solver`) - rust-lang/rust#163508 (Document the `rustc_on_unimplemented` attribute.) - rust-lang/rust#163794 (Use `target_family = "wasm"` instead of `target_arch = "wasm32"`) - rust-lang/rust#163863 (use the type name instead of `Self` in constructor paths again) - rust-lang/rust#163864 (Remove CLAUDE.md) - rust-lang/rust#163877 (Add regression test for duplicated rustdoc search results between std and core) - rust-lang/rust#163916 (Shrink `PartialRes` and its alignment) - rust-lang/rust#149753 (On name resolution error in parameter list, suggest possible `const` typo and avoid unnecessary second error) - rust-lang/rust#152557 (Oneshot `is_ready`) - rust-lang/rust#157273 (Stabilize `optimize` attribute) - rust-lang/rust#162000 (peel_transparent_wrappers only works on non-1ZST) - rust-lang/rust#163343 (`unit` and `[1 x unit]` layouts are incompatible on big-endian targets) - rust-lang/rust#163348 (perf:cache FFI safety results in improper_ctypes lint) - rust-lang/rust#163768 (Move more `rustdoc-html` tests in the right location) - rust-lang/rust#163778 (check is_indirect_first_projection when replacing in RefProp) - rust-lang/rust#163789 (cg_llvm: Avoid `as_c_char_ptr` in several places) - rust-lang/rust#163807 (Add `has_reliable_f16b` for Arm) - rust-lang/rust#163809 (Switch TLS implementation for wasi and bump SDK version to 34) - rust-lang/rust#163826 (Update books) - rust-lang/rust#163849 (ci: update to PowerShell 7.6.6) - rust-lang/rust#163869 (INSTALL.md: use UCRT64 instead of MINGW64 in MSYS2 section) - rust-lang/rust#163870 (Add if-installed:auto:spellcheck to pre-push script)

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rust-bors Bot pushed a commit that referenced this pull request Oct 7, 2026

Auto merge of #163916 - joshtriplett:partialres-shrink, r=<try>

7035dc6

Shrink `PartialRes` and its alignment

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JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 25 pull requests #163919

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JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 24 pull requests #163934

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JonathanBrouwer mentioned this pull request Oct 7, 2026

Rollup of 23 pull requests #163957

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rust-bors Bot merged commit 76f5c92 into rust-lang:main Oct 8, 2026
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rustbot added this to the 1.101.0 milestone Oct 8, 2026

joshtriplett deleted the partialres-shrink branch October 8, 2026 06:46

github-actions Bot mentioned this pull request Oct 9, 2026

Toolchain upgrade to nightly-2026-10-09 flux-rs/flux#1811

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Shrink `PartialRes` and its alignment - #163916

Shrink `PartialRes` and its alignment#163916
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Overall result: ✅ improvements - no action needed

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