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Date: Fri, 30 Mar 2012 11:15:01 -0500 (CDT)
From: Christoph Lameter <cl@linux.com>
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To: KOSAKI Motohiro <kosaki.motohiro@gmail.com>
cc: lwoodman@redhat.com, linux-mm@kvack.org,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Rik van Riel <riel@redhat.com>, Motohiro Kosaki <mkosaki@redhat.com>
Subject: Re: [PATCH -mm] do_migrate_pages() calls migrate_to_node() even if
 task is already on a correct node
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On Thu, 29 Mar 2012, KOSAKI Motohiro wrote:

> >
> > 		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.

Isnt this the original code by Paul? I would think that the 1-1 movement
is only useful to do if the number of nodes in both the destination and
the source is the same.