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

[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()?

Thanks,

Thomas