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Date:   Fri, 27 Apr 2018 19:36:19 +0200
From:   Gerald Schaefer <>
To:     Zi Yan <>
        Zi Yan <>,
        Vineet Gupta <>,,
        Russell King <>,
        Christoffer Dall <>,
        Marc Zyngier <>,,
        Catalin Marinas <>,
        Will Deacon <>,
        Steve Capper <>,
        Kristina Martsenko <>,
        Dan Williams <>,
        Thomas Gleixner <>,
        Ingo Molnar <>,
        "Kirill A. Shutemov" <>,, Ralf Baechle <>,
        James Hogan <>,
        Michal Hocko <>,,
        Benjamin Herrenschmidt <>,
        Paul Mackerras <>,
        Michael Ellerman <>,
        "Aneesh Kumar K.V" <>,
        Ram Pai <>,
        Balbir Singh <>,
        Naoya Horiguchi <>,,
        Martin Schwidefsky <>,
        Heiko Carstens <>,
        Janosch Frank <>,,
        "David S. Miller" <>,, "Huang, Ying" <>
Subject: Re: [RFC PATCH 0/9] Enable THP migration for all possible

On Thu, 26 Apr 2018 10:27:55 -0400
Zi Yan <> wrote:

> From: Zi Yan <>
> Hi all,
> THP migration is only enabled on x86_64 with a special
> ARCH_ENABLE_THP_MIGRATION macro. This patchset enables THP migration for
> all architectures that uses transparent hugepage, so that special macro can
> be dropped. Instead, THP migration is enabled/disabled via
> /sys/kernel/mm/transparent_hugepage/enable_thp_migration.
> I grepped for TRANSPARENT_HUGEPAGE in arch folder and got 9 architectures that
> are supporting transparent hugepage. I mechanically add __pmd_to_swp_entry() and
> __swp_entry_to_pmd() based on existing __pte_to_swp_entry() and
> __swp_entry_to_pte() for all these architectures, except tile which is going to
> be dropped.

This will not work on s390, the pmd layout is very different from the pte
layout. Using __swp_entry/type/offset() on a pmd will go horribly wrong.
I currently don't see a chance to make this work for us, so please make/keep
this configurable, and do not configure it for s390.


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