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Date: Fri, 11 Feb 2022 12:56:24 -0400 From: Jason Gunthorpe <jgg@...dia.com> To: David Hildenbrand <david@...hat.com> Cc: Alex Sierra <alex.sierra@....com>, akpm@...ux-foundation.org, Felix.Kuehling@....com, linux-mm@...ck.org, rcampbell@...dia.com, linux-ext4@...r.kernel.org, linux-xfs@...r.kernel.org, amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org, hch@....de, jglisse@...hat.com, apopple@...dia.com, willy@...radead.org Subject: Re: [PATCH v6 01/10] mm: add zone device coherent type memory support 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
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