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

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Date:   Wed, 9 Nov 2016 23:52:25 +0000
From:   Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:     Anshuman Khandual <khandual@...ux.vnet.ibm.com>
CC:     "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "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" <linux-kernel@...r.kernel.org>,
        "Naoya Horiguchi" <nao.horiguchi@...il.com>
Subject: Re: [PATCH v2 00/12] mm: page migration enhancement for thp

Hi Anshuman,

On Wed, Nov 09, 2016 at 04:03:04PM +0530, Anshuman Khandual wrote:
> 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 ?

Thank you for the suggestion.
I think that's helpful, so will try it in next version.

> 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 ?

I don't have test cases which compare thp migration and split-then-migration
with some numbers. Maybe measuring/comparing the overhead of migration is
a good start point, although I think the real benefit of thp migration comes
from workload "after migration" by avoiding thp split.

Thanks,
Naoya Horiguchi