linux-kernel - Re: [PATCH 28/40] autonuma: make khugepaged pte

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Date:	Thu, 12 Jul 2012 17:25:44 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Andrea Arcangeli <aarcange@...hat.com>
CC:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Hillf Danton <dhillf@...il.com>, Dan Smith <danms@...ibm.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>, Paul Turner <pjt@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Mike Galbraith <efault@....de>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Bharata B Rao <bharata.rao@...il.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Johannes Weiner <hannes@...xchg.org>,
	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>,
	Christoph Lameter <cl@...ux.com>,
	Alex Shi <alex.shi@...el.com>,
	Mauricio Faria de Oliveira <mauricfo@...ux.vnet.ibm.com>,
	Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
	Don Morris <don.morris@...com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Subject: Re: [PATCH 28/40] autonuma: make khugepaged pte_numa aware

On 07/12/2012 02:50 PM, Andrea Arcangeli wrote:
> On Mon, Jul 02, 2012 at 12:24:36AM -0400, Rik van Riel wrote:
>> On 06/28/2012 08:56 AM, Andrea Arcangeli wrote:
>>> If any of the ptes that khugepaged is collapsing was a pte_numa, the
>>> resulting trans huge pmd will be a pmd_numa too.
>>
>> Why?
>>
>> If some of the ptes already got faulted in and made really
>> resident again, why do you want to incur a new NUMA fault
>> on the newly collapsed hugepage?
>
> If we don't set pmd_numa on the collapsed hugepage, the result is that
> we'll understimate the thread NUMA affinity to the node where the
> hugepage is located (mm affinity is recorded independently by the NUMA
> hinting page faults).
>
> If it's better or worse I guess depends on luck, we just lose
> information.

Fair enough.




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