linux-ext4 - Re: [PATCH v6 01/10] mm: add zone device coherent type memory support

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Date:   Fri, 11 Feb 2022 17:49:08 +0100
From:   David Hildenbrand <david@...hat.com>
To:     Jason Gunthorpe <jgg@...dia.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 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.


-- 
Thanks,

David / dhildenb