chore: diagnose the retained heap test on GitHub runners

Author: unadlib

.github/workflows/diag.yml

@@ -0,0 +1,28 @@
+name: Diag memory test
+on:
+  push:
+    branches: [diag/memory-test-flake]
+jobs:
+  diag:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        shard: [1, 2, 3, 4, 5, 6]
+    steps:
+    - uses: actions/checkout@v7
+    - uses: pnpm/action-setup@v6
+    - uses: actions/setup-node@v7
+      with:
+        node-version: 24.x
+        cache: pnpm
+    - run: |
+        pnpm install --frozen-lockfile
+        pnpm build
+        pnpm benchmark:immer:build
+        node --version
+        nproc
+        export DIAG_FILE="$RUNNER_TEMP/diag.jsonl"
+        for i in $(seq 40); do pnpm test:benchmarks > /dev/null 2>&1 || echo "run $i failed"; done
+        for i in $(seq 40); do node --expose-gc --test perf-testing/memory.test.mjs > /dev/null 2>&1 || echo "alone $i failed"; done
+        node -e 'const l=require("fs").readFileSync(process.env.DIAG_FILE,"utf8").trim().split("\n").map(JSON.parse);const d=l.map(x=>x.delta).sort((a,b)=>a-b);console.log("n",d.length,"min",d[0],"max",d[d.length-1]);for(const x of l)if(Math.abs(x.delta)>8192)console.log(JSON.stringify(x))'

.github/workflows/nodejs.yml

@@ -1,6 +1,8 @@
 import assert from 'node:assert/strict';
 import { Session } from 'node:inspector';
 import { performance } from 'node:perf_hooks';
+import v8 from 'node:v8';
+const spaces = () => Object.fromEntries(v8.getHeapSpaceStatistics().map((s) => [s.space_name, s.space_used_size]));
 
 export function allocatedBytes(node) {
   return (
@@ -64,6 +66,7 @@ export async function measureMemory(
   globalThis.gc();
   const gcAfterRetainMs = performance.now() - gcStart;
   const retained = process.memoryUsage();
+  const retainedSpaces = spaces();
   // Observe the contents after measurement, keeping every output live through GC.
   // Patches retain the last tuple per iteration. Avoid storing an output in a
   // separate local, which would keep it alive after clearing the holder.
@@ -74,6 +77,11 @@ export async function measureMemory(
   outputs.fill(null);
   globalThis.gc();
   const released = process.memoryUsage();
+  const releasedSpaces = spaces();
+  globalThis.gc();
+  const released2 = process.memoryUsage();
+  globalThis.gc();
+  const released3 = process.memoryUsage();
   return {
     iterations,
     samplingInterval,
@@ -91,5 +99,6 @@ export async function measureMemory(
     gcAfterRetainMs,
     releasedHeapDeltaBytes: released.heapUsed - before.heapUsed,
     snapshots: { before, batchEnd, retained, released },
+    diag: { retainedSpaces, releasedSpaces, released2: released2.heapUsed, released3: released3.heapUsed },
   };
 }

.github/workflows/npm-publish.yml

@@ -46,6 +46,11 @@ test('retained-output heap excludes persistent cache growth during the pass', as
     },
     { iterations: 16, samplingInterval: 256, warmup: 5 }
   );
+  {
+    const d = metrics.diag;
+    const diff = Object.fromEntries(Object.keys(d.retainedSpaces).map((k) => [k, d.retainedSpaces[k] - d.releasedSpaces[k]]).filter(([, v]) => v));
+    (await import('node:fs')).appendFileSync(process.env.DIAG_FILE ?? '/dev/null', JSON.stringify({ delta: metrics.retainedHeapDeltaBytes, r: metrics.snapshots.retained.heapUsed, rel: metrics.snapshots.released.heapUsed, rel2: d.released2, rel3: d.released3, diff }) + '\n');
+  }
   assert.equal(cache.length, 65536);
   assert.ok(metrics.postGcHeapDeltaBytes > 400 * 1024);
   assert.ok(Math.abs(metrics.retainedHeapDeltaBytes) < 32 * 1024);