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From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Subject: [PATCH] mm: shmem: enable thp migration (Re: [PATCH v1] mm:
 consider non-anonymous thp as unmovable page)
Date: Fri, 6 Apr 2018 03:07:11 +0000
Message-ID: <20180406030706.GA2434@hori1.linux.bs1.fc.nec.co.jp>
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To: Michal Hocko <mhocko@kernel.org>
Cc: "Kirill A. Shutemov" <kirill@shutemov.name>, Zi Yan <zi.yan@sent.com>, "linux-mm@kvack.org" <linux-mm@kvack.org>, Andrew Morton <akpm@linux-foundation.org>, Vlastimil Babka <vbabka@suse.cz>, "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>

Hi everyone,

On Thu, Apr 05, 2018 at 06:03:17PM +0200, Michal Hocko wrote:
> On Thu 05-04-18 18:55:51, Kirill A. Shutemov wrote:
> > On Thu, Apr 05, 2018 at 05:05:47PM +0200, Michal Hocko wrote:
> > > On Thu 05-04-18 16:40:45, Kirill A. Shutemov wrote:
> > > > On Thu, Apr 05, 2018 at 02:48:30PM +0200, Michal Hocko wrote:
> > > [...]
> > > > > RIght, I confused the two. What is the proper layer to fix that t=
hen?
> > > > > rmap_walk_file?
> > > >=20
> > > > Maybe something like this? Totally untested.
> > >=20
> > > This looks way too complex. Why cannot we simply split THP page cache
> > > during migration?
> >=20
> > This way we unify the codepath for archictures that don't support THP
> > migration and shmem THP.
>=20
> But why? There shouldn't be really nothing to prevent THP (anon or
> shemem) to be migratable. If we cannot migrate it at once we can always
> split it. So why should we add another thp specific handling all over
> the place?

If thp migration works fine for shmem, we can keep anon/shmem thp to
be migratable and we don't need any ad-hoc workaround.
So I wrote a patch to enable it.
This patch does not change any shmem specific code, so I think that
it works for file thp (not only shmem,) but I don't test it yet.

Thanks,
Naoya Horiguchi
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