OOM Error When Creating Many ShadowRealms with Heap Snapshots in Node.js

Why this is a good first issue

Memory management issue involving ShadowRealm and heap snapshots requires deep Node.js internals knowledge.

AI Summary

The issue involves an Out of Memory (OOM) error when creating many ShadowRealms and taking heap snapshots in Node.js. The interaction between ShadowRealm creation and heap snapshotting appears to prevent effective garbage collection. This requires understanding of Node.js memory management and ShadowRealm internals.

Issue Description

Version

24.13.1, 25.8.1

Platform

Linux KContainer 5.10.0-12-amd64 #1 SMP Debian 5.10.103-1 (2022-03-07) x86_64 x86_64 x86_64 GNU/Linux

Subsystem

No response

What steps will reproduce the bug?

The below PoC can reproduce the result

import { writeHeapSnapshot } from 'v8';

// This script simulates creating many ShadowRealms and taking heap snapshots

async function main() {
  if (typeof ShadowRealm === 'undefined') {
    console.error('ShadowRealm is not available in this Node build');
    process.exit(1);
  }

  const realms = [];

  for (let i = 0; i < 20000; i++) {
    const realm = new ShadowRealm();
    realms.push(realm);

    // Take heap snapshots periodically
    if (i % 500 === 0) {
      writeHeapSnapshot(`heap-${i}.heapsnapshot`);
      console.log('Created ShadowRealm and heap snapshot at iteration', i);
    }
  }

  console.log('Total ShadowRealms created:', realms.length);
}

main();

How often does it reproduce? Is there a required condition?

No special condition

What is the expected behavior? Why is that the expected behavior?

Even though many objects are allocated, the runtime should handle memory pressure gracefully. The interaction between ShadowRealm creation and heap snapshotting appears to prevent effective garbage collection.

What do you see instead?

root@KContainer:~/49572# node --experimental-shadow-realm --max-old-space-size=1024 test-heapdump-shadow-realm.mjs
Created ShadowRealm and heap snapshot at iteration 0
Created ShadowRealm and heap snapshot at iteration 500

<--- Last few GCs --->

[6100:0x7db2000]    40950 ms: Mark-Compact 995.6 (1033.9) -> 987.2 (1052.6) MB, pooled: 0 MB, 438.54 / 0.00 ms  (average mu = 0.552, current mu = 0.272) allocation failure; scavenge might not succeed
[6100:0x7db2000]    41755 ms: Mark-Compact (reduce) 1002.5 (1054.6) -> 996.6 (1028.6) MB, pooled: 0 MB, 109.72 / 0.01 ms  (+ 572.7 ms in 115 steps since start of marking, biggest s