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

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Message-ID: <4F74BB67.30703@gmail.com>
Date:	Thu, 29 Mar 2012 15:43:35 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	lwoodman@...hat.com
CC:	Christoph Lameter <cl@...ux.com>,
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	linux-mm@...ck.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...hat.com>,
	Motohiro Kosaki <mkosaki@...hat.com>, kosaki.motohiro@...il.com
Subject: Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if
 task is already on a correct node

(3/29/12 2:00 PM), Larry Woodman wrote:
> On 03/22/2012 03:30 PM, Christoph Lameter wrote:
>> On Thu, 22 Mar 2012, Larry Woodman wrote:
>>
>>>> Application may manage their locality given a range of nodes and each of
>>>> the x .. x+n nodes has their particular purpose.
>>> So to be clear on this, in that case the intention would be move 3 to 4, 4 to
>>> 5 and 5 to 6
>>> to keep the node ordering the same?
>> Yup. Have a look at do_migrate_pages and the descrition in the comment by
>> there by Paul Jackson.
>>
>>
> Christoph and others what do you think about this???
>
>
> 		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 */
>+			if ((nodes_weight(*from_nodes) != nodes_weight(*to_nodes)) &&
>+						(node_isset(s, *to_nodes)))
>+				continue;
>+
> 			d = node_remap(s, *from_nodes, *to_nodes);
> 			if (s == d)
> 				continue;

I'm confused. Could you please explain why you choose nodes_weight()? On my first impression,
it seems almostly unrelated factor.


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