linux-kernel - Re: [PATCH] drm/gem: remove obsolete BUG

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Message-ID: <CANq1E4T4=4Sx85_zWVNhH=LYPXWwSaxEAHAG=rdB7GkGwok=ow@mail.gmail.com>
Date:	Sun, 25 May 2014 14:36:30 +0200
From:	David Herrmann <dh.herrmann@...il.com>
To:	David Herrmann <dh.herrmann@...il.com>,
	"dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
	Rob Clark <robdclark@...il.com>,
	Dave Airlie <airlied@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>
Cc:	Daniel Vetter <daniel.vetter@...ll.ch>
Subject: Re: [PATCH] drm/gem: remove obsolete BUG_ON

Hi

On Wed, May 21, 2014 at 3:17 PM, Daniel Vetter <daniel@...ll.ch> wrote:
> On Wed, May 21, 2014 at 02:16:26PM +0200, David Herrmann wrote:
>> The shmem subsystem supports relocating pages on swap-in in case it was
>> loaded into the wrong zone. This was implemented 2 years ago in:
>>
>>     commit bde05d1ccd512696b09db9dd2e5f33ad19152605
>>     Author: Hugh Dickins <hughd@...gle.com>
>>     Date:   Tue May 29 15:06:38 2012 -0700
>>
>>         shmem: replace page if mapping excludes its zone
>>
>> If a driver requires pages to be in a specific zone, they _must_ set the
>> correct GFP flags (like __GFP_DMA32) in mapping_gfp_mask(mapping). shmem
>> will make sure that any page leaving the swap-cache is located in a
>> compatible zone.
>>
>> Signed-off-by: David Herrmann <dh.herrmann@...il.com>
>
> Imo the BUG_ON is nice since we want to make sure this never blows up. We
> have a similar one in i915_gem.c since we do have platforms with 32bit
> limits that support more than 4G or ram.
>
> Imo better to update the comment and state that this is fixed now, but
> better be paranoid.

Ok, I've kept the BUG_ON. I've also appended some more patches that
clean-up the shmem handling. v2 is on the list.

Thanks
David
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