[cairo] Bovine photographs!

[Chris Wilson]

Hi all,

I've been messing around trying to improve performance of my drm-i915
backend and decided it was time to start caching clones. As this is the
same mechanism as is required for caching snapshots, I thought I'd take
another look at snapshot-cow. So whilst I continue to beat upon it, I'd
appreciate for a few more eyes to check it over.

There are two patches (the first to add snapshot-cow, and the second to
use it in the PDF backend to only emit unique patterns) at the tip of
http://cgit.freedesktop.org/~ickle/cairo/

Additionally there is a patch at the tip of
http://cgit.freedesktop.org/~ickle/cairo/commit/?h=drm which uses the
mechanism to provide a clone-similar cache.

I need to review Paolo Bonzini's work on snapshot+cache to see if this
mechanism is applicable to his approach.
-ickle