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    SubjectRe: [PATCH] mm: shmem: enable thp migration (Re: [PATCH v1] mm: consider non-anonymous thp as unmovable page)
    On Wed, 11 Apr 2018 11:26:11 +0200 Michal Hocko <mhocko@kernel.org> wrote:

    > On Fri 06-04-18 03:07:11, Naoya Horiguchi wrote:
    > > >From e31ec037701d1cc76b26226e4b66d8c783d40889 Mon Sep 17 00:00:00 2001
    > > From: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    > > Date: Fri, 6 Apr 2018 10:58:35 +0900
    > > Subject: [PATCH] mm: enable thp migration for shmem thp
    > >
    > > My testing for the latest kernel supporting thp migration showed 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.
    > >
    > > In memory offline code, memory blocks containing unmovable pages should
    > > be prevented from being offline targets by has_unmovable_pages() inside
    > > start_isolate_page_range().
    > >
    > > So it's possible to change migratability
    > > for non-anonymous thps to avoid the issue, but it introduces more complex
    > > and thp-specific handling in migration code, so it might not good.
    > >
    > > So this patch is suggesting to fix the issue by enabling thp migration
    > > for shmem thp. Both of anon/shmem thp are migratable so we don't need
    > > precheck about the type of thps.
    > >
    > > Fixes: commit 72b39cfc4d75 ("mm, memory_hotplug: do not fail offlining too early")
    > > Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
    > > Cc: stable@vger.kernel.org # v4.15+
    >
    > I do not really feel qualified to give my ack but this is the right
    > approach for the fix. We simply do expect that LRU pages are migrateable
    > as well as zone_movable pages.
    >
    > Andrew, do you plan to take it (with Kirill's ack).
    >

    Sure. What happened with "Michal's fix in another email"
    (https://lkml.kernel.org/r/20180406051452.GB23467@hori1.linux.bs1.fc.nec.co.jp)?

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