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

[Mel Gorman <mgorman@suse.de>]

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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