723324 - The "js-gc-heap-chunk-dirty-unused" memory report is occasionally negative

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect)

Description

[Nicholas Nethercote [inactive]]

Occasionally this report goes negative:

    -16,384 B ── js-gc-heap-chunk-dirty-unused [?!]

Steps to reproduce:
- Open about:memory?verbose
- Click the "Update" button over and over.  Eventually you'll see it, though it may take dozens of clicks.

The JS memory multi-reporter doesn't just get the GC lock once and then take all its measurements.  Instead it gets and releases the GC lock multiple times, doing some measurements each time.  And "js-gc-heap-chunk-dirty-unused" is derived from lots of other measurements.

I bet if we just got the GC lock once in CollectRuntimeStats() this problem would go away.

Comment 1

[Guilherme Lima]

This reporter doesn't exist anymore, does it?

Comment 2

[Nicholas Nethercote [inactive]]

> This reporter doesn't exist anymore, does it?

Not with that name.  Something similar still gets measured in the js-main-runtime-gc-heap-committed/ tree, but the problem with the locks may well be gone.  Close enough to close this bug, I think.