linux-kernel - Re: [PATCH 2/6] mempolicy: Kill all mempolicy sharing

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Message-ID: <20120530194858.GW27374@one.firstfloor.org>
Date:	Wed, 30 May 2012 21:48:59 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Christoph Lameter <cl@...ux.com>
Cc:	kosaki.motohiro@...il.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, Andrew Morton <akpm@...gle.com>,
	Dave Jones <davej@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	stable@...r.kernel.org, hughd@...gle.com,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Andrew Morton <akpm@...ux-foundation.org>, andi@...stfloor.org
Subject: Re: [PATCH 2/6] mempolicy: Kill all mempolicy sharing

On Wed, May 30, 2012 at 02:41:22PM -0500, Christoph Lameter wrote:
> On Wed, 30 May 2012, kosaki.motohiro@...il.com wrote:
> 
> > refcount will be decreased even though was not increased whenever alloc_page_vma()
> > is called. As you know, mere mbind(MPOL_MF_MOVE) calls alloc_page_vma().
> 
> Most of these issues are about memory migration and shared memory. If we
> exempt shared memory from memory migration (after all that shared memory
> has its own distinct memory policies already!) then a lot of these issues
> wont arise.

Soft memory offlining needs migration. It's fairly important that this
works: on the database systems most memory is in shared memory and they
have a lot of memory, so predictive failure analysis and soft offlining
helps a lot.

Classic migration is probably not too important here, but they pretty
much rely on the same low level mechanism.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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