linux-kernel - Re: [PATCH] mm: Work around Intel SNB GTT bug with some physical pages.

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Message-ID: <20120508172352.GQ4802@phenom.ffwll.local>
Date:	Tue, 8 May 2012 19:23:52 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	rob.clark@...aro.org
Cc:	Stéphane Marchesin <marcheu@...omium.org>,
	olofj@...omium.org, linux-kernel@...r.kernel.org,
	dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] mm: Work around Intel SNB GTT bug with some physical
 pages.

On Tue, May 08, 2012 at 08:25:38AM -0700, Linus Torvalds wrote:
> On Mon, May 7, 2012 at 4:13 PM, Stéphane Marchesin <marcheu@...omium.org> wrote:
> >
> > In the end, I came up with the ugly workaround of just leaking the
> > offending pages in shmem.c.
> 
> Don't leak it.
> 
> Instead, add it to some RCU list, and free it using RCU. Or some
> one-second timer or something.
> 
> That kind of approach should guarantee that it
> 
>  (a) gets returned to the system
> 
> but
> 
>  (b) the returning to the system gets delayed sufficiently that if the
> i915 driver is doing lots of allocations it will be getting other
> pages.
> 
> Hmm?

The problem is also that this only affects Sandybdrige gpus, so we'd need
to funnel this down to shmfs somehow ... Rob Clarke from Linaro will be
working on a gemfs to make backing storage allocation more flexible - they
need that to support some arm gpus. That way round we wouldn't need to put
some ugly drm/i915 stuff into core shmfs. Rob?
-Daniel
-- 
Daniel Vetter
Mail: daniel@...ll.ch
Mobile: +41 (0)79 365 57 48
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