mm: sched: numa: Control enabling and disabling of NUMA balancing

This patch adds Kconfig options and kernel parameters to allow the
enabling and disabling of automatic NUMA balancing. The existance
of such a switch was and is very important when debugging problems
related to transparent hugepages and we should have the same for
automatic NUMA placement.

Signed-off-by: Mel Gorman <mgorman@suse.de>
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 4b57786..7a02a20 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -811,6 +811,9 @@
 {
 	struct task_struct *p = current;
 
+	if (!sched_feat_numa(NUMA))
+		return;
+
 	/* FIXME: Allocate task-specific structure for placement policy here */
 
 	/*