Re: [PATCH 2/2] drm/i915: Unpin stolen pages

[Chris Wilson <chris@chris-wilson.co.uk>]

On Sat, Jun 01, 2013 at 03:13:04PM +0200, Daniel Vetter wrote:
> On Sat, Jun 1, 2013 at 1:34 PM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> > On Sat, Jun 01, 2013 at 11:17:10AM +0200, Daniel Vetter wrote:
> >> On Sat, Jun 1, 2013 at 1:51 AM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> >> > That neatly explains the WARN. Not too happy about accumulating lots of
> >> > backing storage specific processing into free_object, but that can be
> >> > fixed up later (there is an obj->ops->release() pending).
> >>
> >> I'm more irked with the semantic overloading of object pinning. Might
> >> be cleaner to otherwise mark stolen obejcts as not shrinkable instead
> >> of pinning them for their entire lifetime. But we can bikeshed that
> >> later on ;-)
> >
> > Some merit to that argument, but it still feels correct to say that the
> > stolen pages are pinned for their lifetime. Given obj->ops->release(),
> > it does actually become simpler to not mess around with pin_count. So
> > later it is.
> 
> I was more unhappy that pin_count has different meanings, until I've
> noticed that we've fixed that up already with the introduction of
> ->pages_pin_count. Shouldn't stolen mem just hold a reference on that
> one? After all unbinding from the gtt is ok with stolen memory, but
> dropping the backing storage in the shrinker won't work. Not that we
> currently use stolen for anything else than permanently pinned bos.

As mentioned on irc, stolen does use the pages_pin_count for its
purposes. The purpose of this patch is purely to allow sanity checking
the pages_pin_count with a WARN_ON during free which seems sensible but
not strictly required.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre