730447 - GC: Create a real counter for malloc bytes

Status: RESOLVED FIXED

(Core :: JavaScript Engine, defect)

Description

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

Attachment: patch

This is work toward bug 681479.

Right now we do a GC whenever 100MB of malloc memory has been allocated. This patch tries to improve this heuristic. It keeps a count of how many malloc bytes are allocated at any time. This requires that callers of free know how many bytes are being freed. It seems like in all the important cases, we know this. Once we know how many malloc bytes there are, we can use the usual heuristic of GCing when malloc bytes reach lastMallocBytes*3.

The big advantage of this approach is that we can track any malloc bytes, even if they're very short-lived. The check whether to do a GC or not happens in MaybeGC. So even if lots of memory is allocated and then quickly freed, it won't cause a GC as long as a MaybeGC doesn't happen in between.

I'm hoping this will allow people in Gecko to inform the JS engine of all malloc bytes, regardless of whether they're GCable or not. This should help a lot in cases where a GC would free lots of objects, but we're just not smart enough to GC right now.

Comment 1

[David Mandelin [:dmandelin]]

Thanks for doing this--we've had several bad GC bugs in the past because of the old, inaccurate, accounting.

Comment 2

[Gregor Wagner [:gwagner]]

Comment on attachment 600527 [details] [diff] [review]
patch

Where is triggerMallocGC used?

Comment 3

[Bill McCloskey [inactive unless it's an emergency] (:billm)]

https://hg.mozilla.org/integration/mozilla-inbound/rev/e4f70bd4f96d

I took out triggerMallocGC. It wasn't supposed to be there.

Comment 4

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/e4f70bd4f96d