[PATCH v6 01/10] mm: add zone device coherent type memory support

[Jason Gunthorpe]

On Fri, Feb 11, 2022 at 05:49:08PM +0100, David Hildenbrand wrote:
> On 11.02.22 17:45, Jason Gunthorpe wrote:
> > On Fri, Feb 11, 2022 at 05:15:25PM +0100, David Hildenbrand wrote:
> > 
> >> ... I'm pretty sure we cannot FOLL_PIN DEVICE_PRIVATE pages
> > 
> > Currently the only way to get a DEVICE_PRIVATE page out of the page
> > tables is via hmm_range_fault() and that doesn't manipulate any ref
> > counts.
> 
> Thanks for clarifying Jason! ... and AFAIU, device exclusive entries are
> essentially just pointers at ordinary PageAnon() pages. So with DEVICE
> COHERENT we'll have the first PageAnon() ZONE_DEVICE pages mapped as
> present in the page tables where GUP could FOLL_PIN them.

This is my understanding

Though you probably understand what PageAnon means alot better than I
do.. I wonder if it really makes sense to talk about that together
with ZONE_DEVICE which has alot in common with filesystem originated
pages too.

I'm not sure what AMDs plan is here, is there an expecation that a GPU
driver will somehow stuff these pages into an existing anonymous
memory VMA or do they always come from a driver originated VMA?

Jason