linux-kernel - Re: [PATCH v2 00/12] mm: page migration enhancement for thp

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Message-Id: <5822FB60.5040905@linux.vnet.ibm.com>
Date:   Wed, 9 Nov 2016 16:03:04 +0530
From:   Anshuman Khandual <khandual@...ux.vnet.ibm.com>
To:     Naoya Horiguchi <n-horiguchi@...jp.nec.com>, linux-mm@...ck.org
Cc:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Hugh Dickins <hughd@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...el.com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Vlastimil Babka <vbabka@...e.cz>,
        Pavel Emelyanov <xemul@...allels.com>,
        Zi Yan <zi.yan@...rutgers.edu>,
        Balbir Singh <bsingharora@...il.com>,
        linux-kernel@...r.kernel.org,
        Naoya Horiguchi <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp

On 11/08/2016 05:01 AM, Naoya Horiguchi wrote:
> Hi everyone,
> 
> I've updated thp migration patches for v4.9-rc2-mmotm-2016-10-27-18-27
> with feedbacks for ver.1.
> 
> General description (no change since ver.1)
> ===========================================
> 
> This patchset enhances page migration functionality to handle thp migration
> for various page migration's callers:
>  - mbind(2)
>  - move_pages(2)
>  - migrate_pages(2)
>  - cgroup/cpuset migration
>  - memory hotremove
>  - soft offline
> 
> The main benefit is that we can avoid unnecessary thp splits, which helps us
> avoid performance decrease when your applications handles NUMA optimization on
> their own.
> 
> The implementation is similar to that of normal page migration, the key point
> is that we modify a pmd to a pmd migration entry in swap-entry like format.

Will it be better to have new THP_MIGRATE_SUCCESS and THP_MIGRATE_FAIL
VM events to capture how many times the migration worked without first
splitting the huge page and how many time it did not work ? Also do you
have a test case which demonstrates this THP migration and kind of shows
its better than the present split and move method ?