Re: [RFC 3/3] drm/xe: Add DRM_XE_GEM_CREATE_FLAG_PINNED flag and implementation

[Maarten Lankhorst]

Hey,

Den 2025-08-19 kl. 18:22, skrev Thomas Hellström:
> Hi, Maarten,
> 
> On Tue, 2025-08-19 at 13:49 +0200, Maarten Lankhorst wrote:
>> Add an option to pin memory through the science of cgroup accounting.
>> A bo will be pinned for its entire lifetime, and this allows buffers
>> that are pinned for dma-buf export without requiring the pinning to
>> be
>> done at the dma-buf layer for all devices.
>>
>> For now only implement VRAM pinning. Dave Airlie has a series to
>> implement
>> memcg accounting for the GPU but that is not ready yet.
> 
> Previous discussions around this have favoured a UAPI where we pin a
> gpu-vm range, with a pin at mapping time, or dma-buf pin time where
> required, this allows for dynamic pinning and unpinning, and would
> avoid having separate pinning interfaces for bos and userptr.
> 
> In particular if we don't know at bo creation time which buffer objects
> will be exported with a method requiring pinning, how would UMD deduce
> what buffer objects to pin?
> 
> Thanks,
> Thomas
> For discussion purposes, it seems compute preferred pinning at allocation time,
so I wanted to propose that solution since it's easiest to implement.

I will change it for the next version, but I'm very interested in feedback
on the adjustments I made in cgroups. Those are the ones that will have the
most impact, and changes how effective min/low is calculated when memory
pinned is involved.

Kind regards,
~Maarten