sched/numa: Use group's max nid as task's preferred nid

From task_numa_placement, always try to consolidate the tasks
in a group on the group's top nid.

In case this task is part of a group that is interleaved over
multiple nodes, task_numa_migrate will set the task's preferred
nid to the best node it could find for the task, so this patch
will cause at most one run through task_numa_migrate.

Signed-off-by: Rik van Riel <riel@redhat.com>
Cc: mgorman@suse.de
Cc: chegu_vinod@hp.com
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Peter Zijlstra <peterz@infradead.org>
Link: http://lkml.kernel.org/r/1403538095-31256-2-git-send-email-riel@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>

kernel/sched/fair.c

@@ -1594,23 +1594,8 @@ static void task_numa_placement(struct task_struct *p)
 
 	if (p->numa_group) {
 		update_numa_active_node_mask(p->numa_group);
-		/*
-		 * If the preferred task and group nids are different,
-		 * iterate over the nodes again to find the best place.
-		 */
-		if (max_nid != max_group_nid) {
-			unsigned long weight, max_weight = 0;
-
-			for_each_online_node(nid) {
-				weight = task_weight(p, nid) + group_weight(p, nid);
-				if (weight > max_weight) {
-					max_weight = weight;
-					max_nid = nid;
-				}
-			}
-		}
-
 		spin_unlock_irq(group_lock);
+		max_nid = max_group_nid;
 	}
 
 	if (max_faults) {