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Date:   Tue, 3 Apr 2018 09:59:28 +0200
From:   Michal Hocko <mhocko@kernel.org>
To:     Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        Vlastimil Babka <vbabka@suse.cz>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v1] mm: consider non-anonymous thp as unmovable page
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On Tue 03-04-18 13:46:28, Naoya Horiguchi wrote:
> My testing for the latest kernel supporting thp migration found out an
> infinite loop in offlining the memory block that is filled with shmem
> thps.  We can get out of the loop with a signal, but kernel should
> return with failure in this case.
> 
> What happens in the loop is that scan_movable_pages() repeats returning
> the same pfn without any progress. That's because page migration always
> fails for shmem thps.

Why does it fail? Shmem pages should be movable without any issues.

-- 
Michal Hocko
SUSE Labs