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Date:   Fri, 27 Apr 2018 19:36:19 +0200
From:   Gerald Schaefer <gerald.schaefer@de.ibm.com>
To:     Zi Yan <zi.yan@sent.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Zi Yan <zi.yan@cs.rutgers.edu>,
        Vineet Gupta <vgupta@synopsys.com>,
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        linux-arm-kernel@lists.infradead.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        Steve Capper <steve.capper@arm.com>,
        Kristina Martsenko <kristina.martsenko@arm.com>,
        Dan Williams <dan.j.williams@intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
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        "David S. Miller" <davem@davemloft.net>,
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Subject: Re: [RFC PATCH 0/9] Enable THP migration for all possible
 architectures
In-Reply-To: <20180426142804.180152-1-zi.yan@sent.com>
References: <20180426142804.180152-1-zi.yan@sent.com>
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On Thu, 26 Apr 2018 10:27:55 -0400
Zi Yan <zi.yan@sent.com> wrote:

> From: Zi Yan <zi.yan@cs.rutgers.edu>
> 
> 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.

Regards,
Gerald