Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp
To: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>, linux-mm@kvack.org
References: <1478561517-4317-1-git-send-email-n-horiguchi@ah.jp.nec.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Hugh Dickins <hughd@google.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Dave Hansen <dave.hansen@intel.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Michal Hocko <mhocko@kernel.org>, Vlastimil Babka <vbabka@suse.cz>,
        Pavel Emelyanov <xemul@parallels.com>, Zi Yan <zi.yan@cs.rutgers.edu>,
        Balbir Singh <bsingharora@gmail.com>, linux-kernel@vger.kernel.org,
        Naoya Horiguchi <nao.horiguchi@gmail.com>
From: Anshuman Khandual <khandual@linux.vnet.ibm.com>
Date: Wed, 9 Nov 2016 16:03:04 +0530
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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 ?