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Date:   Mon, 11 Jan 2021 17:15:47 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Jason Gunthorpe <jgg@ziepe.ca>
Cc:     John Hubbard <jhubbard@nvidia.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linux-MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Yu Zhao <yuzhao@google.com>, Andy Lutomirski <luto@kernel.org>,
        Peter Xu <peterx@redhat.com>,
        Pavel Emelyanov <xemul@openvz.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Mike Rapoport <rppt@linux.vnet.ibm.com>,
        Minchan Kim <minchan@kernel.org>,
        Will Deacon <will@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Hugh Dickins <hughd@google.com>,
        "Kirill A. Shutemov" <kirill@shutemov.name>,
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        Kirill Tkhai <ktkhai@virtuozzo.com>,
        Nadav Amit <nadav.amit@gmail.com>, Jens Axboe <axboe@kernel.dk>
Subject: Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse
Message-ID: <20210111161547.GD22493@dhcp22.suse.cz>
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On Mon 11-01-21 12:05:49, Jason Gunthorpe wrote:
> On Sun, Jan 10, 2021 at 11:26:57PM -0800, John Hubbard wrote:
> 
> > So:
> > 
> > FOLL_PIN: would use DMA_PIN_COUNTING_BIAS to increment page refcount.
> > These are long term pins for dma.
> > 
> > FOLL_GET: would use GUP_PIN_COUNTING_BIAS to increment page refcount.
> > These are not long term pins.
> 
> Do we have any places yet that care about the long-term-ness?

I was hoping to use that information to distinguish ephemeral migration
failures due to page reference from long term pins. The later would be a
hard failure for the migration.

-- 
Michal Hocko
SUSE Labs