670283 - throw away cycle collector hash table immediately after MarkRoots()

Status: RESOLVED WONTFIX

(Core :: XPCOM, defect)

Description

[Andrew McCreight [:mccr8]]

As I wrote in Bug 665995, njn found that the CC hash table uses more memory than the CC graph, in at least one run.  The CC hash table is only needed until MarkRoots() is finished, but is kept alive through ScanRoots() and FinishTraverse() as well.  If we introduce a new block scope that ends after MarkRoots (and fuss around with the code a bit) we can free the hash table earlier.  Probably not a huge win, but it should be pretty easy to do.

Comment 1

[Andrew McCreight [:mccr8]]

One drawback of this is that doing it will require changing the indentation for a lot of BeginCollection(), which will totally trash blame.

Comment 2

[:Gavin Sharp [email: [e-mail]]]

"trash blame" is an overstatement - just means that tracking blame for that part of the file will involve one more step (in a process that often takes more than one step anyways).

Comment 3

[Andrew McCreight [:mccr8]]

Yeah that's true.  I just mostly don't like the ugly diff this mostly simple change will produce.

Comment 4

[Andrew McCreight [:mccr8]]

This basically just reduces memory usage during ScanRoots, but ScanRoots barely takes any time ever, so this change is probably not worth bothering with right now.