linux-kernel - Re: [PATCH 1/8] THP: Use real address for NUMA policy

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Date:	Wed, 28 Aug 2013 11:32:19 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Alex Thorlton <athorlton@....com>,
	"Kirill A. Shutemov" <kirill@...temov.name>,
	Dave Hansen <dave.hansen@...el.com>,
	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>,
	"Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	"Eric W . Biederman" <ebiederm@...ssion.com>,
	Sedat Dilek <sedat.dilek@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Dave Jones <davej@...hat.com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	"Paul E . McKenney" <paulmck@...ux.vnet.ibm.com>,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Al Viro <viro@...iv.linux.org.uk>,
	Oleg Nesterov <oleg@...hat.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Kees Cook <keescook@...omium.org>,
	Robin Holt <robinmholt@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>
Subject: Re: [PATCH 1/8] THP: Use real address for NUMA policy

On Wed, Aug 28, 2013 at 11:18:14AM +0200, Ingo Molnar wrote:
> But ideally THP should detect cases where a hugepage is heavily used from 
> multiple nodes and un-HP the page in question. Or not turn it into a 
> hugepage in the first place. (We actually have a memory access pattern 
> sampling facility in place upstream, the new CONFIG_NUMA_BALANCING=y code, 
> which could in theory be utilized.)

Mel and I spoke about doing just that a few weeks ago. Breaking up THP
pages when we get shared faults from different nodes and avoiding
coalescing when the pages are from different nodes.

Rik seemed a little skeptical about the entire thing saying that the
huge tlb gain is about the same order as the locality thing -- while
this is more or less true for the 'tiny' machines most of us have, this
is clearly not the case for these big machines.
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