1814520 - Add support back for allocation tracking with GC types

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, task, P2)

Description

[Ryan Hunt [:rhunt]]

Bug 1814519 temporarily is removing support for allocation tracking of GC types while we're optimizing our allocation performance. We'll need to add a dynamic fallback to support allocation tracking for GC types.

Comment 1

[BugBot [:suhaib / :marco/ :calixte]]

The severity field is not set for this bug.
:rhunt, could you have a look please?

For more information, please visit auto_nag documentation.

Comment 2

[Ryan Hunt [:rhunt]]

Did your struct/array allocation perf patches address this? I think they do a fallback to C++ if their is a AllocationMetadataBuilder on the JSContext, but do we then actually call it?

Comment 3

[Ben Visness [:bvisness]]

Our MacroAssembler code for wasm structs/arrays increments AllocSite::nurseryAllocCount (see all), and the C++ paths (e.g. here) call site->incAllocCount(). I'm not sure if there is more tracking that needs to be done; I'm not familiar with the whole metadata system.

Comment 4

[Ryan Hunt [:rhunt]]

The code I was thinking of is the AllocationMetadataBuilder [1] which is a hook that external code (like devtools) can install to add metadata per-object allocated in the system. This was removed to get us a short term perf win, but now that we have better JIT support we should be able to add it back in as a slow path.

So essentially in our JIT code we'd add another check here [2] that sees if cx->allocationMetadataBuilder is enabled, and if so falls back to C++ code. Then in the C++ code we'd wrap our allocation like this [3], and that would set metadata correctly.

[1] https://searchfox.org/mozilla-central/rev/a06d5a8871b1796f2dbd588ab518eaa98507e018/js/src/vm/Realm.h#915
[2] https://searchfox.org/mozilla-central/rev/a06d5a8871b1796f2dbd588ab518eaa98507e018/js/src/jit/MacroAssembler.cpp#6830
[3] https://searchfox.org/mozilla-central/rev/a06d5a8871b1796f2dbd588ab518eaa98507e018/js/src/builtin/MapObject.cpp#741

Comment 5

[Ryan Hunt [:rhunt]]

I think this will be useful for profiling Dart and other wasm-GC benchmarks to see where all the allocation is coming from.

Comment 7

[Ryan Hunt [:rhunt]]

Attachment: Bug 1814520 - wasm: Support allocation metadata builder for wasm-gc objects. r?bvisness

Comment 8

[Pulsebot]

Pushed by [e-mail]:
https://github.com/mozilla-firefox/firefox/commit/6e6de1ca1a87
https://hg.mozilla.org/integration/autoland/rev/aedd67f498a5
wasm: Support allocation metadata builder for wasm-gc objects. r=bvisness

Comment 9

[pstanciu]

https://hg.mozilla.org/mozilla-central/rev/aedd67f498a5