netdev - Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL

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Message-ID: <20191104204828.GC7731@redhat.com>
Date:   Mon, 4 Nov 2019 15:48:28 -0500
From:   Jerome Glisse <jglisse@...hat.com>
To:     David Rientjes <rientjes@...gle.com>
Cc:     John Hubbard <jhubbard@...dia.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        Alex Williamson <alex.williamson@...hat.com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Björn Töpel <bjorn.topel@...el.com>,
        Christoph Hellwig <hch@...radead.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Daniel Vetter <daniel@...ll.ch>,
        Dave Chinner <david@...morbit.com>,
        David Airlie <airlied@...ux.ie>,
        "David S . Miller" <davem@...emloft.net>,
        Ira Weiny <ira.weiny@...el.com>, Jan Kara <jack@...e.cz>,
        Jason Gunthorpe <jgg@...pe.ca>, Jens Axboe <axboe@...nel.dk>,
        Jonathan Corbet <corbet@....net>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Paul Mackerras <paulus@...ba.org>,
        Shuah Khan <shuah@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>, bpf@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, kvm@...r.kernel.org,
        linux-block@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-kselftest@...r.kernel.org,
        linux-media@...r.kernel.org, linux-rdma@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, netdev@...r.kernel.org,
        linux-mm@...ck.org, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN

On Mon, Nov 04, 2019 at 12:33:09PM -0800, David Rientjes wrote:
> 
> 
> On Sun, 3 Nov 2019, John Hubbard wrote:
> 
> > Introduce pin_user_pages*() variations of get_user_pages*() calls,
> > and also pin_longterm_pages*() variations.
> > 
> > These variants all set FOLL_PIN, which is also introduced, and
> > thoroughly documented.
> > 
> > The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> > to FOLL_PIN:
> > 
> >     pin_user_pages()
> >     pin_user_pages_remote()
> >     pin_user_pages_fast()
> > 
> >     pin_longterm_pages()
> >     pin_longterm_pages_remote()
> >     pin_longterm_pages_fast()
> > 
> > All pages that are pinned via the above calls, must be unpinned via
> > put_user_page().
> > 
> 
> Hi John,
> 
> I'm curious what consideration is given to what pageblock migrate types 
> that FOLL_PIN and FOLL_LONGTERM pages originate from, assuming that 
> longterm would want to originate from MIGRATE_UNMOVABLE pageblocks for the 
> purposes of anti-fragmentation?

We do not control page block, GUP can happens on _any_ page that is
map inside a process (anonymous private vma or regular file back one).

Cheers,
Jérôme