Memory usage (external) reports a negative value?

[bertlea]

• Version: v10.5.0
• Platform: Linux PZW2 4.9.35+ doc: add documentation for AtExit hook #1014 Fri Jun 30 14:34:49 BST 2017 armv6l GNU/Linux
• Subsystem: REPL in Node.js

Running some http server process in node.js in REPL environment (under tmux), the function: process.memoryUsage() function can return a negative value. Is that a bug? The process (server) was run for many days, and I sometimes use process.memoryUsage() to check the values and I found:

> process.memoryUsage()
{ rss: 33452032,
  heapTotal: 9031680,
  heapUsed: 5112064,
  external: -503806 }

The external memory is negative, but it was still postive 2 days ago when I checked. Notes, I run the node.js with flags:

--expose-gc --max-old-space-size=256

This is running on a Raspberry Pi ZERO W.

---

[bnoordhuis]

That probably means you're using an add-on (a native module) with a bug in it - it's miscalling v8::Isolate::AdjustAmountOfExternalAllocatedMemory().

If you can track this down to Node.js core (i.e., exclude add-ons), let me know and I'll reopen.

[bertlea]

OK, I will try to remove all external modules and run the basic functions of the server to try. However, I did not observed that issue on the identical server code ran on version 6.x.x and 8.x.x. Anyway, I will try to run a sample cut-down server without any external module.

[bertlea]

@bnoordhuis I track it down that it got the issue in Node.js core. I can replicate the case that I can have negative external memory from "process.memoryUsage()" call. The situation is simple: You keep making an https GET request to get some contents from a server and do a frequenct gc() call (the V8 garbage collection call), then the external memory reported will going down even keep going even the value is negative.

I think it affects version 10.4.x (may be earlier) to 10.5.0 (latest version) on at least both Windows 64-bit version and the arm v6l version. I suspect it affects all platforms. I found it do not affect v10.1.0 and earlier version. A simple but not very clean code can show the issue:

Notes: http seems not affected, and also you need to run it with --expose-gc flag.

const https = require('https');
function getip() {
    https.get('https://api.ipify.org', (resp) => {
        let data = '';
        resp.on('data', (chunk) => data += chunk);
        resp.on('end', () => console.log(`data: ${data} ext mem: ${process.memoryUsage().external}`));
        resp.on('error', (err) => console.log('error: ' + err.message));
    });

    gc();    
}

if(typeof gc !== 'function') {
    console.log('gc is not enabled, use --expose-gc flag to run.');
    process.exit();
}

setInterval(getip, 3000); //get ip every 3 seconds
console.log('test started. expecting out every 3 seconds. Ctr-c to quit.');

[bertlea]

Clarification: The issue I tested is at the "client" side that making HTTPS request, not at the server side.

[bnoordhuis]

Thanks, reopened and labels updated.

[bertlea]

Updated the sample code to demo the issue with a simpler code using a public HTTPS service.

[bertlea]

@bnoordhuis Just curious if this is not yet classified as a bug so nobody is looking at it? Or it is low priority and just waiting in some queues? I am not familiar with the process here, but I agree it is not high-priority as it seems not breaking anything other than reporting negative memory sizes.

[logidelic]

FWIW, I've been seeing this on Node 10.9 as well.