External memory leak on node v8.x

[cirias]

• Version: 8.11.2
• Platform: Linux sirius-Alienware-15-R3 4.13.0-41-generic Tracking / Assuring Compatibility #46~16.04.1-Ubuntu SMP Thu May 3 10:06:43 UTC 2018 x86_64 x86_64 x86_64 GNU/Linux

The code below will cause external memory leak of v8 engine. In v8, mark-compact updates the external_memory before the gc, which cause the external_memory_limit too big. Normally, It's fine, we just got a bigger limit. But when scavenge happened before next mc, updated the external_memory, the external_memory_limit will keep increasing.

I thought this issue has already been fixed in these commits, and node v9.x already ported them:
https://codereview.chromium.org/2917853004
https://codereview.chromium.org/2921883002

function triggerScavenge() {
  let arr = [];
  for (let i = 0; i < 5000; i++) {
    arr.push({});
  }

  setTimeout(triggerScavenge, 50);
}

let ds = [];

function triggerMarkCompact() {
  const { rss, heapTotal, heapUsed, external } = process.memoryUsage();
  console.log('------memoryUsage------', rss, heapTotal, heapUsed, external);

  for (let i = 0; i < 1000; i++) {
    ds.push(new ArrayBuffer(1024));
  }

  if (ds.length > 40000) {
    ds = [];
  }

  setTimeout(triggerMarkCompact, 200);
}

triggerScavenge();
triggerMarkCompact();

Run the script with --trace-gc to dump gc info.

Attached a graph of the memory usage

[Trott]

@nodejs/v8

[ofrobots]

The fix came to v9.x in the form of an upgrade to V8 6.1 on #14730.

It needs to be individually back-ported for 8.x. Self-assigning to do this / investigate feasibility once I have some bandwidth, but if anyone else has cycles sooner, please go ahead and re-assign.

[ofrobots]

Backport on #21269.

[ofrobots]

The fix has been merged on 8.x and will be released as part of 8.12.0. Closing.