844009 - Investigate not cleaning up BACKGROUND_HOMESCREEN resources

Status: RESOLVED INVALID

(Core :: General, defect)

Description

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

The two places we do extra work when the homescreen goes to the background are
 - here [1].  This may toss out some caches and initiate what should be light collection of dead objects.
 - here [2].  This will throw out all "onscreen" graphics resources.

If we can get better performance by conditioning these on BACKGROUND_HOMESCREEN, we should consider doing that evaluated against negative consequences.

[1] http://mxr.mozilla.org/mozilla-central/source/dom/ipc/ProcessPriorityManager.cpp#571
[2] http://mxr.mozilla.org/mozilla-central/source/layout/base/nsPresShell.cpp?force=1#9164

Comment 1

[Justin Lebar (not reading bugmail)]

> If we can get better performance by conditioning these on BACKGROUND_HOMESCREEN

What is/are the performance metric/s you're interested in here?  Is it just "time between pressing the home button and the homescreen showing," or is it something else?

Comment 2

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

That's the main one.

Comment 3

[Justin Lebar (not reading bugmail)]

If we can, we should profile what the homescreen is doing after you press the home button.  Is it actually spending a lot of time decoding images?  I don't think the minimize-memory-usage is throwing anything significant away other than images, in this case, but maybe it is, and hopefully we'd see that in the profile.

Comment 4

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Agreed; note, this is an "Investigate ..." bug, not a "Fix ..." one.

Comment 5

[Chris Jones [:cjones] inactive; ni?/f?/r? if you need me]

Might be a nice user-perceivable win in prime real estate, but not proven out yet.

Comment 6

[Florian Bender]

I guess this better applies to this Bug: 

(Florian Bender from Last Comment Bug 823284 comment #11)
> How about capturing the complete last known state of the Homescreen and save
> it as one big image. Then show this image when returning to the homescreen
> until everything else is ready. Is this sensible at all? Will this help?
> Will this reduce or increase memory usage (Note: we may be able to discard
> even more mem data because we have a "saved state" the User sees before
> everything needs to be reparsed/recalculated/repainted)? 
> 
> This may actually work for all apps. And I think iOS does this (at least
> with some apps).