Possible external-memory / GC regression from v22 to v24 in short-lived Readable chunk workloads
まだ誰も着手していません。
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説明
I’m seeing a pretty consistent regression from Node.js v22.22.3 to v24.16.0 on a small stream benchmark that creates lots of short-lived Readables and drains them immediately. The code in the benchmark file benchmark/streams/readable-push-buffer-burst-minimal.js is not optimal, but that's not the point as it demonstrates the issue.
'use strict';
const common = require('../common.js');
const assert = require('assert');
const { Readable } = require('stream');
const bench = common.createBenchmark(main, {
n: [2e4],
bodySize: [120 * 1024],
});
function repeat(size, ch) {
return ch.repeat(size);
}
function makeBurstChunks(bodySize) {
return [
'<!doctype html><html><head><title>burst</title><style>',
repeat(1024, 'a'),
'</style></head><body><header>',
repeat(2048, 'b'),
'</header><main>',
repeat(bodySize, 'c'),
'</main><script>',
repeat(2048, 'd'),
'</script></body></html>',
];
}
function toBuffers(chunks) {
return chunks.map((chunk) => Buffer.from(chunk, 'utf8'));
}
function buildAndDrain(buffersIn) {
const buffersOut = [];
for (let i = 0; i < buffersIn.length; i++) {
const readable = new Readable({ read() {} });
readable.push(buffersIn[i]);
readable.push(null);
let chunk;
while ((chunk = readable.read()) !== null)
buffersOut.push(chunk);
}
return Buffer.concat(buffersOut);
}
function main({ n, bodySize }) {
const inputBuffers = toBuffers(makeBurstChunks(bodySize));
const expectedLength = inputBuffers.reduce(
(sum, chunk) => sum + chunk.length,
0,
);
const warmup = buildAndDrain(inputBuffers);
assert.strictEqual(warmup.length, expectedLength);
bench.start();
for (let i = 0; i < n; ++i) {
const buffer = buildAndDrain(inputBuffers);
if (buffer.length !== expectedLength)
throw new Error(`Unexpected buffer length: ${buffer.length}`);
}
bench.end(n);
}
So running the benchmark comparing v22.22.3 vs v24.16.0, I see the following results:
$ node benchmark/compare.js --old ~/.nvm/versions/node/v22.22.3/bin/node --new ~/.nvm/versions/node/v24.16.0/bin/node --filter readable-push-buffer-burst-minimal streams > readable-push-buffer-burst-minimal.csv
[00:00:58|% 100| 1/1 files | 60/60 runs | 1/1 configs]: Done
$ npx node-benchmark-compare readable-push-buffer-burst-minimal.csv
confidence improvement accuracy (*) (**) (***)
streams/readable-push-buffer-burst-minimal.js bodySize=122880 n=20000 *** -37.18 % ±4.12% ±5.55% ±7.36%
I also profiled both cases with perf and generated flamegraphs. The main difference seems to be GC behavior: v22 is mostly dominated by scavenges, while v24 is much more major-GC-heavy. See attached flamegraph-22.svg and flamegraph-24.svg.
One more datapoint that seems relevant: if I run v24 with --external-memory-accounted-in-global-limit, the regression drops a lot. Here are the results using a patched benchmark/compare.js that supports per-binary flags:
$ node benchmark/compare.js --old ~/.nvm/versions/node/v22.22.3/bin/node --new ~/.nvm/versions/node/v24.16.0/bin/node --new-flags "--external-memory-accounted-in-global-limit" --filter readable-push-buffer-burst-minimal streams > readable-push-buffer-burst-minimal_with_flag.csv
[00:00:50|% 100| 1/1 files | 60/60 runs | 1/1 configs]: Done
$ npx node-benchmark-compare readable-push-buffer-burst-minimal_with_flag.csv
confidence improvement accuracy (*) (**) (***)
streams/readable-push-buffer-burst-minimal.js bodySize=122880 n=20000 *** -11.18 % ±4.28% ±5.76% ±7.62%
Be aware that when doing many comparisons the risk of a false-positive result increases.
In this case, there are 1 comparisons, you can thus expect the following amount of false-positive results:
0.05 false positives, when considering a 5% risk acceptance (*, **, ***),
0.01 false positives, when considering a 1% risk acceptance (**, ***),
0.00 false positives, when considering a 0.1% risk acceptance (***)
So in summary, when running the benchmark, I see a 37% regression which drops to only 11% when using v24 with the --external-memory-accounted-in-global-limit flag.
Does this ring a bell as a known regression or is this to be expected in v24?
Flamegraphs
- flamegraph-22.svg (
v22.22.3) - flamegraph-24.svg (
v24.16.0) - flamegraph-24-flag.svg (
v24.16.0 --external-memory-accounted-in-global-limit)
/cc @RafaelGSS
コントリビューションガイド
はじめの一歩
- issue を最後まで読み、次にプロジェクトのコントリビューションガイドを読みます。
- 着手することを issue にコメントします — 二人が同じ作業をするのを防げます。
- リポジトリをフォークし、ブランチを切って変更します。
- issue 番号を参照したプルリクエストを送ります。
調査の方向性
まず、2つの Node.js バージョンに対して benchmark/compare.js を使って benchmark/streams/readable-push-buffer-burst-minimal.js を実行し、その後、添付された flamegraph を比較します。GC の挙動の変化と --external-memory-accounted-in-global-limit の影響を調査します。再現可能なベンチマーク結果を根拠として、v22 から v24 への性能差が想定された変更なのか回帰なのかを判断できれば完了です。
索引モデルが issue の本文から書いたものです。
評価
- 技術スタック
- javascript, node.js
- 領域
- backend, performance
- issue の種類
- バグ
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- 4/5
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