729534 - maple: Buffer rotation appears broken on engadget

Status: VERIFIED FIXED

(Core :: Graphics, defect, P1)

Description

[Jeff Muizelaar [:jrmuizel]]

Chris Lord says:
Buffer rotation doesn't appear to be working. At least on Engadget, I'm
constantly seeing huge uploads when scrolling a small amount.

Comment 1

[Chris Lord [:cwiiis]]

Just to note, it appears broken on pretty much every site to a certain degree, but Engadget is particularly badly affected.

Comment 2

[Chris Lord [:cwiiis]]

Attachment: Fix retaining layers when the displaylist children of a scroll layer change

roc debugged this with me yesterday, and we(...he) discovered that buffer rotation isn't being used effectively on Engadget because we don't seem to be retaining layers as we scroll down the page.

This is because the frame used to retain a layer when there are multiple children of a scroll layer is the last one, which has a tendency to change. This patch makes it use the first child instead, which tends to be more stable.

The proper fix would be to associate it with a frame that definitely won't change, but this is a low-risk quick fix that I imagine helps in the majority of cases (and certainly fixes the engadget.com case).

This has a dramatic effect on performance for Maple.

Comment 3

[Chris Lord [:cwiiis]]

For reference, a try run looks good: https://tbpl.mozilla.org/?tree=Try&rev=bf681c51d65e

Comment 4

[Chris Lord [:cwiiis]]

Comment on attachment 601563 [details] [diff] [review]
Fix retaining layers when the displaylist children of a scroll layer change

Changing reviewer to mats, given that roc was the one that came up with the fix.

Comment 5

[Mats Palmgren (inactive)]

Comment on attachment 601563 [details] [diff] [review]
Fix retaining layers when the displaylist children of a scroll layer change

Seems a bit random, but if it works better, sure.  r=mats
Add a XXX comment and file a bug on making a proper fix?

Comment 6

[Chris Lord [:cwiiis]]

Attachment: Fix retaining layers when the displaylist children of a scroll layer change

Attaching final committed patch for reference.

Comment 7

[Joe Drew (not getting mail)]

https://hg.mozilla.org/projects/maple/rev/d137bbd5fe5b

Chris, make sure you file a proper fix and link it from this bug.

Comment 8

[Chris Lord [:cwiiis]]

The proper fix is filed as bug 731641 (and the comment checked in mentions this also).

Comment 9

[Marco Bonardo [:mak]]

https://hg.mozilla.org/mozilla-central/rev/fc1d914138a0

Comment 10

[Cristian Nicolae (:xti)]

Verified fixed on:

Firefox 15.0a1 (2012-05-29)
Firefox 14.0a2 (2012-05-29)

Device: Galaxy Nexus
OS: Android 4.0.2