linux-kernel - Re: [PATCH 7/8] sched: Split accounting of NUMA hinting faults that pass two-stage filter

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Message-ID: <20130628101245.GD8362@linux.vnet.ibm.com>
Date:	Fri, 28 Jun 2013 15:42:45 +0530
From:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mel Gorman <mgorman@...e.de>, 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 7/8] sched: Split accounting of NUMA hinting faults that
 pass two-stage filter

> > 
> > > Ideally it would be possible to distinguish between NUMA hinting faults
> > > that are private to a task and those that are shared. This would require
> > > that the last task that accessed a page for a hinting fault would be
> > > recorded which would increase the size of struct page. Instead this patch
> > > approximates private pages by assuming that faults that pass the two-stage
> > > filter are private pages and all others are shared. The preferred NUMA
> > > node is then selected based on where the maximum number of approximately
> > > private faults were measured.
> > 
> > Should we consider only private faults for preferred node?
> 
> I don't think so; its optimal for the task to be nearest most of its pages;
> irrespective of whether they be private or shared.

Then the preferred node should have been chosen based on both the
private and shared faults and not just private faults.

> 
> > I would think if tasks have shared pages then moving all tasks that share
> > the same pages to a node where the share pages are around would be
> > preferred. No? 
> 
> Well no; not if there's only 5 shared pages but 1024 private pages.

Yes, agree, but should we try to give the shared pages some additional weightage?

-- 
Thanks and Regards
Srikar Dronamraju

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