linux-kernel - [PATCH 0/1] mm/migrate: do not call prep_transhuge_page if !thp_migration

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Date:   Mon, 20 Nov 2017 16:17:29 +0000
From:   Andrea Reale <ar@...ux.vnet.ibm.com>
To:     linux-kernel@...r.kernel.org, zi.yan@...rutgers.edu,
        n-horiguchi@...jp.nec.com
Cc:     akpm@...ux-foundation.org, jglisse@...hat.com, realean2@...ibm.com
Subject: [PATCH 0/1] mm/migrate: do not call prep_transhuge_page if
 !thp_migration_supported

Hi all,

While working on a second round of patches to introduce memory hotplug /
hot remove to arm64 (original attempt at [1]), and trying to rebase them
on 4.14, I stumbled in some problematic behaviour during page migration
when offlining for hot remove, whereas target pages for migration where
found in a bad state.

I believe that this behaviour may be originating from commit 8135d8926c08
("mm: memory_hotplug: memory hotremove supports thp migration")
and it is triggered when migrating pages for builds that have no
ARCH_ENABLE_THP_MIGRATION but have thp support on (arm64, in my case).
Specifically, my understanding is that prep_transhuge_page should not be
called in linux/migrate.h:new_page_nodemask if !thp_migration_supported
because, in that case, new_page would not be a thp.

A tiny patch follows, showing what I mean. Please, let me know if my
understanding is bogus.

Best regards,
Andrea

[1] https://lkml.org/lkml/2017/4/11/536

Andrea Reale (1):
  mm/migrate: do not call prep_transhuge_page if
    !thp_migration_supported

 include/linux/migrate.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

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