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Date: Fri, 12 Oct 2012 07:37:50 -0400
From: Rik van Riel <riel@redhat.com>
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Subject: Re: [PATCH 23/33] autonuma: retain page last_nid information in khugepaged
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To: Mel Gorman <mel@csn.ul.ie>
Cc: Andrea Arcangeli <aarcange@redhat.com>, linux-kernel@vger.kernel.org, linux-mm@kvack.org, Linus Torvalds <torvalds@linux-foundation.org>, Andrew Morton <akpm@linux-foundation.org>, Peter Zijlstra <pzijlstr@redhat.com>, Ingo Molnar <mingo@elte.hu>, Hugh Dickins <hughd@google.com>, Johannes Weiner <hannes@cmpxchg.org>, Hillf Danton <dhillf@gmail.com>, Andrew Jones <drjones@redhat.com>, Dan Smith <danms@us.ibm.com>, Thomas Gleixner <tglx@linutronix.de>, Paul Turner <pjt@google.com>, Christoph Lameter <cl@linux.com>, Suresh Siddha <suresh.b.siddha@intel.com>, Mike Galbraith <efault@gmx.de>, "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, Bharata B Rao <bharata.rao@gmail.com>, Lee Schermerhorn <Lee.Schermerhorn@hp.com>, Srivatsa Vaddagiri <vatsa@linux.vnet.ibm.com>, Alex Shi <alex.shi@intel.com>, Mauricio Faria de Oliveira <mauricfo@linux.vnet.ibm.com>, Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>, Don Morris <don.morris@hp.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>

On 10/11/2012 02:44 PM, Mel Gorman wrote:
> On Thu, Oct 04, 2012 at 01:51:05AM +0200, Andrea Arcangeli wrote:
>> When pages are collapsed try to keep the last_nid information from one
>> of the original pages.
>>
>
> If two pages within a THP disagree on the node, should the collapsing be
> aborted? I would expect that the code of a remote access exceeds the
> gain from reduced TLB overhead.

Hard to predict.  The gains from THP seem to be on the same
order as the gains from NUMA locality, both between 5-15%
typically.

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