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Date: Mon, 4 Nov 2019 15:48:28 -0500
From: Jerome Glisse <jglisse@redhat.com>
To: David Rientjes <rientjes@google.com>
Subject: Re: [PATCH v2 05/18] mm/gup: introduce pin_user_pages*() and FOLL_PIN
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On Mon, Nov 04, 2019 at 12:33:09PM -0800, David Rientjes wrote:
>=20
>=20
> On Sun, 3 Nov 2019, John Hubbard wrote:
>=20
> > Introduce pin_user_pages*() variations of get_user_pages*() calls,
> > and also pin_longterm_pages*() variations.
> >=20
> > These variants all set FOLL_PIN, which is also introduced, and
> > thoroughly documented.
> >=20
> > The pin_longterm*() variants also set FOLL_LONGTERM, in addition
> > to FOLL_PIN:
> >=20
> >     pin_user_pages()
> >     pin_user_pages_remote()
> >     pin_user_pages_fast()
> >=20
> >     pin_longterm_pages()
> >     pin_longterm_pages_remote()
> >     pin_longterm_pages_fast()
> >=20
> > All pages that are pinned via the above calls, must be unpinned via
> > put_user_page().
> >=20
>=20
> Hi John,
>=20
> I'm curious what consideration is given to what pageblock migrate types=
=20
> that FOLL_PIN and FOLL_LONGTERM pages originate from, assuming that=20
> longterm would want to originate from MIGRATE_UNMOVABLE pageblocks for th=
e=20
> 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,
J=E9r=F4me