[PATCH v2 09/15] drm/ttm, drm/amdgpu: Allow the driver some control over swapping

[Christian König]

Am 18.05.21 um 17:15 schrieb Thomas Hellström:
>
> On 5/18/21 10:26 AM, Thomas Hellström wrote:
>> We are calling the eviction_valuable driver callback at eviction time to
>> determine whether we actually can evict a buffer object.
>> The upcoming i915 TTM backend needs the same functionality for swapout,
>> and that might actually be beneficial to other drivers as well.
>>
>> Add an eviction_valuable call also in the swapout path. Try to keep the
>> current behaviour for all drivers by returning true if the buffer object
>> is already in the TTM_PL_SYSTEM placement. We change behaviour for the
>> case where a buffer object is in a TT backed placement when swapped out,
>> in which case the drivers normal eviction_valuable path is run.
>>
>> Finally export ttm_tt_unpopulate() and don't swap out bos
>> that are not populated. This allows a driver to purge a bo at
>> swapout time if its content is no longer valuable rather than to
>> have TTM swap the contents out.
>>
>> Cc: Christian König <christian.koenig at amd.com>
>> Signed-off-by: Thomas Hellström <thomas.hellstrom at linux.intel.com>
>
> Christian,
>
> Here we have a ttm_tt_unpopulate() export as well at the end. I figure 
> you will push back on that one. What we really need is a functionality 
> to just drop the bo contents and end up in system memory unpopulated. 
> Should I perhaps add a utility function to do that instead? like 
> ttm_bo_purge()?

We already have that. Just call ttm_bo_validate() without any place to 
put the buffer.

See how ttm_bo_pipeline_gutting() is used.

Christian.

>
> Thanks,
>
> Thomas
>
>