Re: [PATCH 06/23] drm/xe/svm: Introduce a helper to build sg table from hmm range

[Jason Gunthorpe <jgg@nvidia.com>]

On Mon, Apr 29, 2024 at 10:25:48AM +0200, Thomas Hellström wrote:

> > Yes there is another common scheme where you bind a window of CPU to
> > a
> > window on the device and mirror a fixed range, but this is a quite
> > different thing. It is not SVA, it has a fixed range, and it is
> > probably bound to a single GPU VMA in a multi-VMA device page table.
> 
> And this above here is exactly what we're implementing, and the GPU
> page-tables are populated using device faults. Regions (large) of the
> mirrored CPU mm need to coexist in the same GPU vm as traditional GPU
> buffer objects.

Well, not really, if that was the case you'd have a single VMA over
the entire bound range, not dynamically create them.

A single VMA that uses hmm_range_fault() to populate the VM is
completely logical.

Having a hidden range of mm binding and then creating/destroying 2M
VMAs dynamicaly is the thing that doesn't make alot of sense.

Jason