wasm-memprof - A heap memory profiler for WebAssembly

A sampling-based heap memory profiler for WebAssembly on JavaScript engines.

Features

• No modification required: You don't need to modify your WebAssembly module to profile memory usage.
• pprof format: The memory profile is saved in the pprof format, which can be visualized by many existing tools.
• Sampling-based: The profiler samples memory allocation stack traces to reduce the overhead.

About

wasm-memprof enables you to profile the heap memory usage of WebAssembly instances without asking you to recompile your WebAssembly module. It instruments your WebAssembly module to intercept memory allocation and deallocation calls, and then collects memory allocation stack traces. All what you need to do is to wrap the WebAssembly object with WMProf.wrap and then you can dump the memory profile to a pprof file.

Installation

npm install wasm-memprof

Usage

import { WMProf } from "wasm-memprof";

const WebAssembly = WMProf.wrap(globalThis.WebAssembly);
const { instance } = await WebAssembly.instantiate(buffer);
instance.exports.myFunction();

// Get profiler instance associated with the WebAssembly instance
const wmprof = WMProf.get(instance);
// Download the pprof profile file to the client
wmprof.downloadSnapshot();
// Or get the pprof profile bytes (Uint8Array)
const pprof = wmprof.snapshot();
fs.writeFileSync(`wmprof-${Date.now()}.pb`, pprof);

// Get all installed profilers
const profilers = WMProf.installed();

Visualize pprof profile results

pprof

You can use the pprof tool to visualize the result.

go tool pprof -http=":8081" ./path/to/wmprof-XXXXX.pb

Speedscope

You can upload the pprof profile file to the speedscope website to visualize the result.

Limitations

1. This profiler currently supports only V8-based JavaScript engines (e.g., Chrome, Chromium-based browsers, Node.js) because it relies on V8's Stack trace API. We are happy to accept contributions to support other JavaScript engines.

2. WebAssembly modules profiled by wasm-memprof must have debug names for their memory allocator functions:

   • malloc
   • free
   • calloc
   • realloc
   • posix_memalign
   • aligned_alloc

   Otherwise, the profiler will not be able to intercept memory allocation and deallocation calls.

Advanced Usage

Demangle language-specific function names

We currently provide only a Swift demangler, but you can implement your own demangler for other languages.

import { WMProf } from "wasm-memprof";
import { SwiftDemangler } from "wasm-memprof/plugins/swift-demangler.js";

const swiftDemangler = SwiftDemangler.create();
const WebAssembly = WMProf.wrap(globalThis.WebAssembly, {
  demangler: swiftDemangler.demangle.bind(swiftDemangler),
});

Capture all allocations without sampling

By default, the profiler samples memory allocations to reduce the overhead. If you want to capture all allocations, you can set the sampleRate option to 1, which means the profiler traces every memory allocation.

import { WMProf } from "wasm-memprof";

const WebAssembly = WMProf.wrap(globalThis.WebAssembly, {
  sampleRate: 1,
});