722715 - [Meta] After starting Firefox and running various asynchronous initialization steps cycle collection graph should stay empty if browser is idle

Status: RESOLVED FIXED

(Core :: General, defect)

Description

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

We should be able to keep the graph empty if CanSkip* methods are very effective
and nothing is creating new garbage.
Things to look at:
- XBL
- XUL protos
- ObserverService

Comment 1

[Andrew McCreight [:mccr8]]

This sounds like a great goal.  Concrete, and it should have a positive overall impact!

Comment 2

[Andrew McCreight [:mccr8]]

We should come up with a set of pages we want to investigate first.  At first guess, I'd imagine that web apps like Gmail and Facebook will be active even when the user is idle.  Should we exclude them from consideration?

Comment 3

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

At first step I want to just open 1 about:blank tab in Firefox and have empty CC graph when
CC is called. This mean that various things which still add script objects to the graph
need to be optimized out.

Comment 4

[Andrew McCreight [:mccr8]]

That does sound like a good starting point.

Comment 5

[Andrew McCreight [:mccr8]]

Attachment: CC log with my latest set of patches

Comment 6

[Andrew McCreight [:mccr8]]

Attachment: CC log with my latest set of patches

I think I didn't actually finish a full recompile with that previous log.  This one looks much better.  Something appears to manage to swoop up the bulk of the XUL prototype nodes.  I'm not sure what that's about.

Comment 7

[Andrew McCreight [:mccr8]]

There are 626 nodes in the graph.  83 nodes by themselves.  64 nodes in pairs, mostly involving nsXPCWrappedJS.  Most of the rest looks like things that are being held alive by the observer service, though there are a few other weird cases, like a global_for_XPCJSContextStack_SafeJSContext.

Comment 8

[Andrew McCreight [:mccr8]]

bug 736563 clears up a few small blobs of about:blank from the graph.

Comment 9

[Andrew McCreight [:mccr8]]

With all the patches in the dependent bugs applied, I'm seeing a CC graph with 494 nodes, with my Gmail + mozilla wiki + error console.

This is the breakdown by size of blob:

1=180(180), 2=49(98), 3=8(24), 4=3(12), 6=1(6), 7=1(7), 8=2(16), 10=2(20), 14=1(14), 16=1(16), 46=1(46), 55=1(55),

The format is blobsize=numOfBlogs(total number of nodes in blobs of that size).

The two largest chunks are the JS Safe Context and a big chunk of script that an nsXULPrototypeNode holds onto.

Comment 10

[Andrew McCreight [:mccr8]]

Attachment: the full CC graph with these patches

Comment 11

[Andrew McCreight [:mccr8]]

There's still some room for improvement of nsXULPrototypeNodes.  In my regular browsing session, there are about 4000 nodes in the graph, and around 1900 of these are in a single blob of JS being traced from an nsXULPrototypeNode.  We could probably add black JS tracing for these somehow.  There are also two other blobs with a hundred or so JS nodes in them that also look like that.

Comment 12

[BugBot [:suhaib / :marco/ :calixte]]

The bug assignee is inactive on Bugzilla, so the assignee is being reset.

Comment 13

[Marco Castelluccio [:marco]]

Sorry, there was a problem with the detection of inactive users. I'm reverting the change.

Comment 14

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

Looks like the bugs this depended on are closed so I can close this too.

We should definitely do new measurements, but let's file new bugs for those.