1837666 - Check the size of metadata with wasm-GC modules

Status: RESOLVED FIXED

(Core :: JavaScript: WebAssembly, task, P3)

Description

[Ryan Hunt [:rhunt]]

We have metadata for wasm modules which consume some memory overhead at runtime and size overhead when serializing the module.

With wasm-GC, modules are going to have many more stackmaps than before. We should make sure we're not blowing up our metadata size.

StackMaps are part of wasm::MetadataTier. They're an ordered list of bitmaps.

One thing we could do as part of this is to land some debug-only size tracking methods for modules. This would make it easier to track this over time.

We do have some 'sizeOf' methods already that are part of our about:memory reporting infrastructure [1]. It'd be nice to re-use those, but they work using a callback provided by our embedders which returns the size of memory blocks allocated using malloc.

[1] https://searchfox.org/mozilla-central/rev/d8c5478bd730644dab4336fdb83271ac1ca1d6b5/js/src/wasm/WasmCode.cpp#706

Comment 1

[Julien Pages [:jpages]]

Here are some statistics about metadata sizes for a collection of wasm programs.

https://docs.google.com/spreadsheets/d/1Ykp-WGXF6dO7ITdpEQh_2TWiGnxFZ6uDUH9RsJiSGJ8/edit?usp=sharing

File size are as follow:
4.9M acrobat.wasm
832K amazon-ivs.wasm
52M autocad.wasm
5.0M bergamot.wasm
6.7M canvaskit.wasm
45M clang.wasm
2.4M dotnet.wasm,
21M earth.wasm
155K element.wasm
16M figma.wasm
366K google-meet-echo.wasm
11M google-meet-media.wasm
21K hyphenopoly-en-us.wasm
8.8M js.wasm
115K libopenjph_simd.wasm
80M photoshop.wasm
11M pspdfkit.wasm
9.1M pyodide.wasm
5.6M ruffle-1.wasm
5.7M ruffle-2.wasm
595K sql.wasm
13M stockfish-nnue.wasm
340K stockfish.wasm
374K tensorflow.wasm
990 ublock-biditrie.wasm
1.1K ublock-hntrie.wasm
1.2K ublock-lz4-block-codec.wasm
408 ublock-publicsuffixlist.wasm
1.7M zoom-audio.wasm
3.0M zoom-video.wasm

Comment 2

[Julien Pages [:jpages]]

In general, metadata size seems to be substantial. Metadata represent a 20 to 30% of generated code size for the baseline compiler.
Ion generates less code but the same amount of metadata, this proportion is even higher with 30 to 40% on average.

Comment 3

[Julien Pages [:jpages]]

Attachment: Bug 1837666 - wasm: Add StackMaps to sizeOfExcludingThis in metadata.

Also add a function to get trap sites length in metadata.

Comment 4

[Julien Pages [:jpages]]

Attachment: Bug 1837666 - wasm: Add an option to analyze metadata size.

Use the --wasm-test-metadata to get an analysis of metadata size.
The wasmMetadataAnalysis() function returns a JS dictionary containing
various statistics related to metadata size.

Depends on D187944

Comment 5

[Julien Pages [:jpages]]

I've updated the statistics here https://docs.google.com/spreadsheets/d/1Ykp-WGXF6dO7ITdpEQh_2TWiGnxFZ6uDUH9RsJiSGJ8/edit?usp=sharing

I've also tried to run the analysis in debug and release, and got the same results (same sizes).

Comment 6

[Julien Pages [:jpages]]

Attachment: profile.js

Here is the script I'm using for collecting statistics in various wasm applications.

Comment 7

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/integration/autoland/rev/e27238af0e74
wasm: Add StackMaps to sizeOfExcludingThis in metadata. r=jseward
https://hg.mozilla.org/integration/autoland/rev/53f39978c827
wasm: Add an option to analyze metadata size. r=jseward

Comment 8

[Cosmin Sabou [:CosminS]]

https://hg.mozilla.org/mozilla-central/rev/e27238af0e74
https://hg.mozilla.org/mozilla-central/rev/53f39978c827