Re: [PATCH drm-misc-next v3 5/7] drm/gpuvm: add an abstraction for a VM / BO combination

Thomas Hellström
2023-09-11T21:19:41Z

Hi, Danilo

On 9/9/23 17:31, Danilo Krummrich wrote:
> This patch adds an abstraction layer between the drm_gpuva mappings of
> a particular drm_gem_object and this GEM object itself. The abstraction
> represents a combination of a drm_gem_object and drm_gpuvm. The
> drm_gem_object holds a list of drm_gpuvm_bo structures (the structure
> representing this abstraction), while each drm_gpuvm_bo contains list of
> mappings of this GEM object.
>
> This has multiple advantages:
>
> 1) We can use the drm_gpuvm_bo structure to attach it to various lists
> of the drm_gpuvm. This is useful for tracking external and evicted
> objects per VM, which is introduced in subsequent patches.
>
> 2) Finding mappings of a certain drm_gem_object mapped in a certain
> drm_gpuvm becomes much cheaper.
>
> 3) Drivers can derive and extend the structure to easily represent
> driver specific states of a BO for a certain GPUVM.
>
> The idea of this abstraction was taken from amdgpu, hence the credit for
> this idea goes to the developers of amdgpu.
>
> Cc: Christian König <christian.koenig@amd.com>
> Signed-off-by: Danilo Krummrich <dakr@redhat.com>

Did you consider having the drivers embed the struct drm_gpuvm_bo in
their own bo definition? I figure that would mean using the gem bo's
refcounting and providing a helper to call from the driver's bo release.
Looks like that could potentially save a lot of code? Or is there
something that won't work with that approach?

Thanks,

Thomas