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

[Dave Airlie]

> Let me know if this understanding is correct.
>
> Or what would you like to do in such situation?
>
> >
> > Not sure how it is really a good idea.
> >
> > Adaptive locality of memory is still an unsolved problem in Linux,
> > sadly.
> >
> > > > However, the migration stuff should really not be in the driver
> > > > either. That should be core DRM logic to manage that. It is so
> > > > convoluted and full of policy that all the drivers should be working
> > > > in the same way.
> > >
> > > Completely agreed. Moving migration infrastructures to DRM is part
> > > of our plan. We want to first prove of concept with xekmd driver,
> > > then move helpers, infrastructures to DRM. Driver should be as easy
> > > as implementation a few callback functions for device specific page
> > > table programming and device migration, and calling some DRM common
> > > functions during gpu page fault.
> >
> > You'd be better to start out this way so people can look at and
> > understand the core code on its own merits.
>
> The two steps way were agreed with DRM maintainers, see here:  https://lore.kernel.org/dri-devel/SA1PR11MB6991045CC69EC8E1C576A715925F2@SA1PR11MB6991.namprd11.prod.outlook.com/, bullet 4)

After this discussion and the other cross-device HMM stuff I think we
should probably push more for common up-front, I think doing this in a
driver without considering the bigger picture might not end up
extractable, and then I fear the developers will just move onto other
things due to management pressure to land features over correctness.

I think we have enough people on the list that can review this stuff,
and even if the common code ends up being a little xe specific,
iterating it will be easier outside the driver, as we can clearly
demark what is inside and outside.

Dave.