[PATCH 8/8] drm/panfrost: Make sure the shrinker does not reclaim referenced BOs

[Steven Price]

On 29/11/2019 16:07, Boris Brezillon wrote:
> On Fri, 29 Nov 2019 15:48:15 +0000
> Steven Price <steven.price at arm.com> wrote:
> 
>> On 29/11/2019 13:59, Boris Brezillon wrote:
>>> Userspace might tag a BO purgeable while it's still referenced by GPU
>>> jobs. We need to make sure the shrinker does not purge such BOs until
>>> all jobs referencing it are finished.
>>>
>>> Fixes: 013b65101315 ("drm/panfrost: Add madvise and shrinker support")
>>> Cc: <stable at vger.kernel.org>
>>> Signed-off-by: Boris Brezillon <boris.brezillon at collabora.com>  
>>
>> I'm happy with this, but I would also argue that it was previously user
>> space's job not to mark a BO purgeable while it's in use by the GPU.
> 
> I was not aware of this design choice.

When I was maintaining mali_kbase I would have said no to this ;) But
thankfully I've moved on! I'm not sure whether anyone actually made a
design choice for Panfrost here.

>> This is in some ways an ABI change so we should be sure this is
>> something that we want to support "forever" more.
> 
> Well, in that case, the ABI change is bringing extra robustness, with
> AFAICT, no downside for those that were taking care of that in
> userspace.

Yes, there's no downside for user space - this is just giving user space
extra freedom.

>> But if Mesa has
>> 'always' been assuming this behaviour we might as well match.
> 
> I think so, and VC4 seems to have the same expectations.

This seems like enough justification to me.

Steve

>>
>> Reviewed-by: Steven Price <steven.price at arm.com>
> 
> Thanks for the review.
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