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

[Larry Woodman <lwoodman@redhat.com>]

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On 04/24/2012 12:19 PM, KOSAKI Motohiro wrote:
>> 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@jp.fujitsu.com>
>
>
>
>> +            if ((nodes_weight(*from_nodes) != 
>> nodes_weight(*to_nodes)) &&
>> +                        (node_isset(s, *to_nodes)))
>> +                continue;
>> +
>
>
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How does this look:



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diff --git a/mm/mempolicy.c b/mm/mempolicy.c
index f563fa3..b76b49a 100644
--- a/mm/mempolicy.c
+++ b/mm/mempolicy.c
@@ -1012,6 +1012,24 @@ 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/there are
+			 * a different number of source and destination nodes,
+			 * never move memory out of a source node that is also
+			 * a destination node.
+			 * 
+			 * Example: [2,3,4] -> [3,4,5] moves everything.
+			 * 	    [0-7] - > [3,4,5] moves only 0,1,2,6,7.
+			 */
+
+			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;