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

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Message-ID: <20130703183517.GC18898@dyad.programming.kicks-ass.net>
Date:	Wed, 3 Jul 2013 20:35:17 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Mel Gorman <mgorman@...e.de>
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 03:21:39PM +0100, Mel Gorman wrote:
> Initial support for automatic NUMA balancing was unable to distinguish
> between false shared versus private pages except by ignoring pages with an
> elevated page_mapcount entirely. This patch kicks away the training wheels
> as initial support for identifying shared/private pages is now in place.
> 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.

This reminds me; there a clause in task_numa_work() that skips 'small' VMAs. I
don't see the point of that.

In fact; when using things like electric fence this might mean skipping most
memory.
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