linux-kernel - Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse

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Date:   Mon, 11 Jan 2021 17:15:47 +0100
From:   Michal Hocko <mhocko@...e.com>
To:     Jason Gunthorpe <jgg@...pe.ca>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Linux-MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Yu Zhao <yuzhao@...gle.com>, Andy Lutomirski <luto@...nel.org>,
        Peter Xu <peterx@...hat.com>,
        Pavel Emelyanov <xemul@...nvz.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Mike Rapoport <rppt@...ux.vnet.ibm.com>,
        Minchan Kim <minchan@...nel.org>,
        Will Deacon <will@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Hugh Dickins <hughd@...gle.com>,
        "Kirill A. Shutemov" <kirill@...temov.name>,
        Matthew Wilcox <willy@...radead.org>,
        Oleg Nesterov <oleg@...hat.com>, Jann Horn <jannh@...gle.com>,
        Kees Cook <keescook@...omium.org>,
        Leon Romanovsky <leonro@...dia.com>, Jan Kara <jack@...e.cz>,
        Kirill Tkhai <ktkhai@...tuozzo.com>,
        Nadav Amit <nadav.amit@...il.com>, Jens Axboe <axboe@...nel.dk>
Subject: Re: [PATCH 0/1] mm: restore full accuracy in COW page reuse

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