[Intel-gfx] [PATCH v3 3/8] drm/i915: Add a new "remapped" gtt_view

[Tvrtko Ursulin]

On 01/10/2018 16:12, Chris Wilson wrote:
> Quoting Ville Syrjälä (2018-10-01 16:03:30)
>> On Wed, Sep 26, 2018 at 08:50:25AM +0100, Tvrtko Ursulin wrote:
>>>
>>> On 25/09/2018 20:37, Ville Syrjala wrote:
>>> One more thing, do you really need random access for this
>>> transformation? Or you could walk the sg list as it is? Just if you hit
>>> a too long chunk you need to copy a trimmed version over and know where
>>> to continue for the next row. If doable it would be better than having
>>> to kvmalloc_array.
>>
>> I think Chris suggested just using i915_gem_object_get_dma_address()
>> here. But I'm not sure why we're not using it for rotate_pages()
>> as well.
> 
> Tvrtko is opposed to populating the obj->mm.pages cache with no defined
> release point. I say the mempressure and shrinker should to the right
> thing, but it's a big if.

Wasn't there some compromise we agreed last time? Like that you would 
just add an API to drop the cache? So users like this one and rotation, 
where it is known to be very unlikely the cache would be used again, 
would be able to drop it immediately after remapping?

But maybe you had an argument that the cache could be used after all? So 
pread/pwrite on framebuffers likely? Relocations wouldn't be. Is there 
something else?

Maybe we should resolve this since it's been going for a very long time. :)

Regards,

Tvrtko