1357813 - Add a "GC Exclusion" mode which suppresses expensive GCs

Status: RESOLVED DUPLICATE of bug 1351790

(Core :: JavaScript: GC, enhancement, P3)

Description

[Kannan Vijayan [:djvj]]

Add a mode to the GC that suppresses (or at least heavily discourages) expensive GCs until the mode is over.

This mode should be used by Gecko for short-lived UX-sensitive operations where we don't want to introduce jank.

Comment 1

[Jon Coppeard (:jonco)]

I'm assuming that this will function as another input into a GC scheduler rather than completely suppressing GCs.

Comment 2

[(no longer active)]

I think the use case here is indeed completely suppressing GC, but the implementation can certainly happen though an input to the scheduler (although I admit that I haven't been able to keep up with the GC scheduler proposals so I don't know to what extent that idea is practical!)

Comment 3

[Jon Coppeard (:jonco)]

(In reply to :Ehsan Akhgari (needinfo please, extremely long backlog) from comment #2)
I'm not keen on the idea of suppressing GC entirely for arbitrary lengths of time because this can lead to OOM.  I'd rather see something that increased the GC thresholds by a configurable factor, maybe as much as a factor of 2.  This would effectively prevent GC in all but the most dire situation.

Do we have a list of places in the browser that this would be used?

Comment 4

[Florian Quèze [:florian]]

(In reply to Jon Coppeard (:jonco) from comment #3)

> Do we have a list of places in the browser that this would be used?

I would like to suppress GCs while opening a new tab or opening a new window (I saw profiles with GCs causing jank in the tab open animation, and delays before first-paint of new windows). But indeed, completely suppressing the GC may not be the best behavior if we do happen to already have plenty of tabs/windows and to lack available memory.

Comment 5

[Olli Pettay [:smaug][[e-mail]]]

Cyclecollector could use this to try to avoid GC triggers when CC is running, since if GC runs then, CC needs to finish its work synchronously.

http://searchfox.org/mozilla-central/rev/4d8e389498a08668cce9ebf6232cc96be178c3e4/xpcom/base/CycleCollectedJSRuntime.cpp#1454,1459
http://searchfox.org/mozilla-central/rev/4d8e389498a08668cce9ebf6232cc96be178c3e4/xpcom/base/nsCycleCollector.cpp#3782,3793

Comment 6

[Jean Gong :jgong]

Moving this to P2 for post 57 work.

Comment 7

[Kannan Vijayan [:djvj]]

This is really a dup.  Both this bug and the other one are about preventing expensive GCs when certain "critical UX" activity is happening, so as the reduce user-perceived jank.  The other one is assigned, so it gets priority.