[Intel-gfx] [PATCH 3/4] drm/i915: Add support for stealing purgable stolen pages

[Chris Wilson]

On Mon, Jul 27, 2015 at 11:38:13AM +0200, Daniel Vetter wrote:
> Chris and I just discussed on irc that the bound_list isn't in a great LRU
> order right now and Chris sent out a fix for that. But it only works if we
> preferrentially shrink inactive objects first. Worth the bother or just a
> FIXME? For the fb use-case alone it's not needed since we can't remove the
> fb until it's no longer being displayed (otherwise the backwards-compat
> code kicks in and synchronously kills the display at RMFB time), and that
> pretty much means we can't put the underlying bo into any cache (and mark
> it purgeable) either. But a FIXME comment here would be good for sure,
> just in case this assumption ever gets broken.

I've been mucking around with patch a bit (with contexts-from-stolen
reenabled) and the list ierators used here are terrible; severely
impacting our allocations by a few orders of magnitude (imagine having
just the ggtt full of 4k objects, let alone several ppgtt all full of
their own bound 4k objetcs).

To combat this will require a special purgeable list maintaind by
madv(), and subclassing the struct drm_mm_node to hold our extra
details.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre