linux-kernel - Re: [PATCH 13/18] mm: numa: Scan pages with elevated page

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Message-ID: <20130731091330.GK2296@suse.de>
Date:	Wed, 31 Jul 2013 10:13:30 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Sam Ben <sam.bennn@...il.com>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...nel.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount

On Wed, Jul 17, 2013 at 01:22:22PM +0800, Sam Ben wrote:
> On 07/15/2013 11:20 PM, Mel Gorman wrote:
> >Currently automatic NUMA balancing is unable to distinguish between false
> >shared versus private pages except by ignoring pages with an elevated
> 
> What's the meaning of false shared?
> 

Two tasks may be operating on a shared buffer that is not aligned. It is
expected that will at least cache align to avoid CPU cache line bouncing
but the buffers are not necessarily page aligned. A page is the minimum
granularity we can track NUMA hinting faults so two tasks sharing
such a page will appear to be sharing data when in fact they are not.

-- 
Mel Gorman
SUSE Labs
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