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

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Message-ID: <0a8799c3-1d4c-8d87-ebca-013f6541fbc4@linux.intel.com>
Date:   Mon, 11 Sep 2023 19:19:09 +0200
From:   Thomas Hellström 
        <thomas.hellstrom@...ux.intel.com>
To:     Danilo Krummrich <dakr@...hat.com>, airlied@...il.com,
        daniel@...ll.ch, matthew.brost@...el.com, sarah.walker@...tec.com,
        donald.robson@...tec.com, boris.brezillon@...labora.com,
        christian.koenig@....com, faith.ekstrand@...labora.com
Cc:     dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH drm-misc-next v3 5/7] drm/gpuvm: add an abstraction for a
 VM / BO combination

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@....com>
> Signed-off-by: Danilo Krummrich <dakr@...hat.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