Date: Wed, 31 Jul 2013 10:13:30 +0100
From: Mel Gorman <mgorman@suse.de>
To: Sam Ben <sam.bennn@gmail.com>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>,
        Srikar Dronamraju <srikar@linux.vnet.ibm.com>,
        Ingo Molnar <mingo@kernel.org>, Andrea Arcangeli <aarcange@redhat.com>,
        Johannes Weiner <hannes@cmpxchg.org>, Linux-MM <linux-mm@kvack.org>,
        LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH 13/18] mm: numa: Scan pages with elevated page_mapcount
Message-ID: <20130731091330.GK2296@suse.de>
References: <1373901620-2021-1-git-send-email-mgorman@suse.de>
 <1373901620-2021-14-git-send-email-mgorman@suse.de>
 <51E62A0E.1070102@gmail.com>
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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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