linux-kernel - Re: [PATCH -mm V2] do_migrate_pages() calls migrate_to_node() even if task is already on a correct node

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Date:	Tue, 24 Apr 2012 12:19:06 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	lwoodman@...hat.com
CC:	linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Christoph Lameter <cl@...ux.com>,
	Motohiro Kosaki <mkosaki@...hat.com>,
	Rik van Riel <riel@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	kosaki.motohiro@...il.com
Subject: Re: [PATCH -mm V2] do_migrate_pages() calls migrate_to_node() even
 if task is already on a correct node

> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 47296fe..6c189fa 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1012,6 +1012,16 @@ int do_migrate_pages(struct mm_struct *mm,
>  		int dest = 0;
>
>  		for_each_node_mask(s, tmp) {
> +
> +			/* IFF there is an equal number of source and
> +			 * destination nodes, maintain relative node distance
> +			 * even when source and destination nodes overlap.
> +			 * However, when the node weight is unequal, never move
> +			 * memory out of any destination nodes */

Please use

/*
  * foo bar
  */

style comment. and this comment only explain how code work but don't explain why.
I hope the comment describe HPC usecase require to migrate if src and dest have the
same weight.

Otherwise looks ok. please feel free to use my ack to your next spin.
  Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>



> +			if ((nodes_weight(*from_nodes) != nodes_weight(*to_nodes)) &&
> +						(node_isset(s, *to_nodes)))
> +				continue;
> +


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