791127 - Mark things held live by documents black during GC, instead of unmarking them later

Status: NEW

(Core :: DOM: Core & HTML, defect, P5)

Description

[Andrew McCreight [:mccr8]]

Right now, we UnmarkGray a bunch of JS things during the first CC cleanup phase after a GC. We could change these to be held as black roots during the GC, which should reduce the time of that initial long CC cleanup phase.

Comment 1

[Andrew McCreight [:mccr8]]

Attachment: part 1: infrastructure

This parameterizes the MarkContentViewer/MarkDocShell/MarkSHEntry/etc. functions over a new class, DocumentVisitor, that has a single callback method that takes a document. It then implements the current cleanupJS etc stuff using it. This patch should not change the behavior.

Comment 2

[Andrew McCreight [:mccr8]]

Once that is in place, you can drop in a chunk of code like this into TraceBlackJS:

+  if (!++nsCCUncollectableMarker::sGeneration) {
+    ++nsCCUncollectableMarker::sGeneration;
+  }
+  GCDocumentVisitor docVisitor(aTrc);
+  MarkLiveWindows(&docVisitor);

...where GCDocumentVisitor is a subclass of DocumentVisitor that uses the JS tracer on things hanging off of the document.

In my measurements in an optimized debug build, this MarkLiveWindows can take a millisecond or two, which will add to the GC time. So that's not super great. It seems to be mostly just iterating over all of the stuff.

Comment 3

[Andrew McCreight [:mccr8]]

Attachment: part 2: mark protos of live docs black, WIP

Comment 4

[Andrew McCreight [:mccr8]]

Attachment: part 3: convert a bunch of cleanupJS to be marked black, WIP

Comment 5

[Firefox Bug Husbandry Bot]

https://bugzilla.mozilla.org/show_bug.cgi?id=1472046

Move all DOM bugs that haven’t been updated in more than 3 years and has no one currently assigned to P5.

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