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

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Date:	Fri, 28 Jun 2013 11:36:25 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
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

On Fri, Jun 28, 2013 at 12:30:27PM +0530, Srikar Dronamraju wrote:
> * Mel Gorman <mgorman@...e.de> [2013-06-26 15:38:06]:
> 
> > 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.

> 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.

> If yes, how does the preferred node logic help to achieve
> the above?

There's no packing logic yet...
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