linux-kernel - Re: [PATCH 36/46] mm: numa: Use a two-stage filter to restrict pages being migrated for unlikely task<->node relationships

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Message-ID: <20121121193908.GN8218@suse.de>
Date:	Wed, 21 Nov 2012 19:39:08 +0000
From:	Mel Gorman <mgorman@...e.de>
To:	Ingo Molnar <mingo@...nel.org>
Cc:	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Hugh Dickins <hughd@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Paul Turner <pjt@...gle.com>,
	Lee Schermerhorn <Lee.Schermerhorn@...com>,
	Alex Shi <lkml.alex@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linux-MM <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 36/46] mm: numa: Use a two-stage filter to restrict pages
 being migrated for unlikely task<->node relationships

On Wed, Nov 21, 2012 at 07:15:47PM +0000, Mel Gorman wrote:
> I've added a note now to that effect now. For all the patches with notes
> or any other ones, I'll be very happy to add the Signed-offs back on if
> the original authors acknowledge they are ok with the end result. If you
> recall, in the original V1 of this series I said;
> 
> 	This series steals very heavily from both autonuma and schednuma
> 	with very little original code. In some cases I removed the
> 	signed-off-bys because the result was too different. I have noted
> 	in the changelog where this happened but the signed-offs can be
> 	restored if the original authors agree.
> 
> Just to compare, this is the wording in "autonuma: memory follows CPU
> algorithm and task/mm_autonuma stats collection"
> 
> +/*
> + * In this function we build a temporal CPU_node<->page relation by
> + * using a two-stage autonuma_last_nid filter to remove short/unlikely
> + * relations.
> + *
> + * Using P(p) ~ n_p / n_t as per frequentest probability, we can
> + * equate a node's CPU usage of a particular page (n_p) per total
> + * usage of this page (n_t) (in a given time-span) to a probability.
> + *
> + * Our periodic faults will then sample this probability and getting
> + * the same result twice in a row, given these samples are fully
> + * independent, is then given by P(n)^2, provided our sample period
> + * is sufficiently short compared to the usage pattern.
> + *
> + * This quadric squishes small probabilities, making it less likely
> + * we act on an unlikely CPU_node<->page relation.
> + */
> 
> If this was the basis for the sched/numa patch then I'd point out that
> I'm not the only person that failed to preserve history perfectly.
> 

Which to be clear, it isn't. The original source is sched/numa according
to https://lkml.org/lkml/2012/8/22/629 

-- 
Mel Gorman
SUSE Labs
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