linux-kernel - Re: [Intel-gfx] [PATCH] drm/i915: Selectively enable self-reclaim

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Date:	Fri, 2 Jul 2010 10:49:47 +1000
From:	Dave Airlie <airlied@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	"M. Vefa Bicakci" <bicave@...eronline.com>,
	Chris Wilson <chris@...is-wilson.co.uk>, earny@...4u.de,
	Roman Jarosz <kedgedev@...il.com>,
	intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
	jcnengel@...glemail.com,
	"A. Boulan" <arnaud.boulan@...ertysurf.fr>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	Pekka Enberg <penberg@...helsinki.fi>,
	A Rojas <nqn1976list@...il.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	rientjes@...gle.com, michael@...nelt.co.at, stable@...nel.org
Subject: Re: [Intel-gfx] [PATCH] drm/i915: Selectively enable self-reclaim

On Fri, Jul 2, 2010 at 10:06 AM, Dave Airlie <airlied@...il.com> wrote:
> On Fri, Jul 2, 2010 at 9:59 AM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
>> On Thu, Jul 1, 2010 at 3:34 PM, M. Vefa Bicakci <bicave@...eronline.com> wrote:
>>>
>>> Based on my testing, I am happy to report that the change you suggest
>>> fixes the "memory corruption (segfaults) after thaw" issue for me.
>>> I can't thank you enough times for this.
>>
>> Hey, goodie. And you're the one to be thanked - bisecting it down to
>> that commit that wasn't _meant_ to have any real semantic changes
>> (except for the bug-fix of racy mapping gfp-flags update) is what
>> really cracked the lid on the problem.
>>
>>> Now, the obligatory question: Could we have this fix applied to 2.6.32,
>>> 2.6.33 and 2.6.34 ?
>>
>> No problem, except we should first determine exactly what flags are
>> the appropriate ones. My original patch was obviously not even
>> compile-tested, and I actually meant for people to use GFP_HIGHUSER
>> rather than __GFP_HIGHMEM. That contains all the "regular" allocation
>> flags (but not the __GFP_MOVABLE, which is still just a suspicion of
>> being the core reason for the problem).
>>
>> And the original DRM code had:
>>
>>   GFP_HIGHUSER |
>>   __GFP_COLD |
>>   __GFP_FS |
>>   __GFP_RECLAIMABLE |
>>   __GFP_NORETRY |
>>   __GFP_NOWARN |
>>   __GFP_NOMEMALLOC
>>
>> which is not entirely sensible (__GFP_FS is already part of
>> GFP_HIGHUSER, for example), and two of the flags (NORETRY and NOWARN)
>> are the ones the driver wants to do conditionally.
>>
>> But that still leaves the question about __GFP_COLD (probably sane),
>> __GFP_RECLAIMABLE (I wonder about that one) and __GFP_NOMEMALLOC
>> (usually used together with NORETRY, and I'm not at all sure it makes
>> sense as a base flag).
>>
>> So I suspect the final patch should not look like the one you tested,
>> but instead likely have
>>
>>   GFP_HIGHUSER | __GFP_COLD
>>
>> and possibly the __GFP_RECLAIMABLE flag too instead of just the bare
>> __GFP_HIGHMEM..
>>
>> (Well, we already had that __GFP_COLD there from before, so it's
>> really about replacing __GFP_HIGHMEM with something like "GFP_HIGHUSER
>> | __GFP_RECLAIMABLE").
>>
>> But its' great to hear that this does seem to be the underlying cause.
>> If you could test with that GFP_HIGHUSER | __GFP_RECLAIMABLE, that
>> would be a good thing. After all - maybe the problem was triggered by
>> some other flag than __GFP_MOVABLE, and as such, having some
>> additional testing with a bigger set of allocation flags would be a
>> really good thing.
>
> I just sent a patch I tested here with GFP_HIGHUSER | __GFP_COLD
> instead, and it resumes okay for me,
>
> I'll play with GFP_RECLAIMABLE now,
>
> If anyone wants to know why nobody uses hibernate, this laptop with a
> 4200rpm driver boots faster than the hibernate cycle.

RECLAIMABLE added also seems fine, of course you can't have
RECLAIMABLE and MOVABLE (I find this out when it oopses on boot).

So I suspect MOVABLE is the problem. but I don't know enough about gfp
flags to know what RECLAIMABLE buys us, and where it  might bite us so
I can test some more.

Dave.
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