commit 9df586b67f3c467b33364f79d4056864bc27cda8
author Benoit Lize <lizeb@chromium.org> Wed Jan 31 10:46:34 2024
committer Benoit Lize <lizeb@chromium.org> Wed Jan 31 10:46:34 2024
tree c66201bf72e7f1e9fd856a18a2d5ec2d639f724e
parent 251950b828b18b26958a639c3578473ea9523cde

[viz] Add a feature to return overlays without frame production

On platforms with delegated compositing, tiles (for instance) are passed
to the display compositor to handle compositing itself. However, by the
time we are swapping to frame N, the tiles of frame N-1 have likely not
been released by the display compositor, since it would need them to
produce a frame if something else happens on screen (outside of
Chromium) at the next VSync.

To make sure that we release resources, we will check these overlays
again when frame N+1, N+2, etc. are swapped, and then we eventually
release the overlays, returning exported resources to the client.

This breaks down... where there is no frame N+1. While this may sound
like a corner case, it happens in practice locally with the browser UI
compositor, which can spend a lot of time without producing a new frame,
or a page with an animation that stops.

On macOS, for a simple page with a large non-looping GIF, this wastes
~30MiB of memory, since tiles for the second to last frame are retained
service-side (because we don't check). Similar cases would happen with
e.g. a fade-in animation, ads with non-repeating animations, or a page
with layout changes during loading (since its tiles would be entirely
dirty). It may also happen with PDF scrolling, since the way we
currently render creates a new set of tiles for each frame. The same
test case shows ~9MiB of memory lost this way for the browser UI
compositor.

This CL fixes the issue by checking 1s later whether the overlays are
still in use, and returning the resources to the client.

Bug: 1503162
Change-Id: I8bffb20aacdbfaa3a17c044d50ca9387dcdef391
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5038622
Reviewed-by: ccameron chromium <ccameron@chromium.org>
Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1254431}