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

[Rob Clark]

On Tue, May 8, 2012 at 12:23 PM, Daniel Vetter <daniel@xxxxxxxx> wrote:
> 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@xxxxxxxxxxxx> 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?

Well, a bit hand-wavey at this point, but the idea is to let the
driver have control of the page allocation via 'struct
address_space_operations'.. but otherwise work in a similar way as
shmfs.

Something like get_xip_mem() is almost what we want, except we don't
want it to populate the pages, we don't want to force a kernel
mapping, and shmem doesn't use it..

I suppose we still need a short term fix for i915, but at least it
would only be temporary.

BR,
-R

> -Daniel
> --
> Daniel Vetter
> Mail: daniel@xxxxxxxx
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