linux-kernel - Re: [PATCH 12/13] mm: numa: Scan pages with elevated page

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Date:	Thu, 4 Jul 2013 10:32:11 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	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 12/13] mm: numa: Scan pages with elevated page_mapcount

On Wed, Jul 03, 2013 at 08:41:24PM +0200, Peter Zijlstra wrote:
> On Wed, Jul 03, 2013 at 03:21:39PM +0100, Mel Gorman wrote:
> 
> > Note that the patch still leaves shared, file-backed in VM_EXEC vmas in
> > place guessing that these are shared library pages. Migrating them are
> > likely to be of major benefit as generally the expectation would be that
> > these are read-shared between caches and that iTLB and iCache pressure is
> > generally low.
> 
> I'm failing to grasp.. we don't migrate them because migrating them would
> likely be beneficial?
> 
> Missing a negative somewhere?

Yes.

Note that the patch does not migrate shared, file-backed within vmas marked
VM_EXEC as these are generally shared library pages. Migrating such pages
is not beneficial as there is an expectation they are read-shared between
caches and iTLB and iCache pressure is generally low.

-- 
Mel Gorman
SUSE Labs
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