mm/numa: Skip NUMA_NO_NODE and online nodes in numa_map_to_online_node()

Update numa_map_to_online_node() to stop falling back to numa node 0
when the input is NUMA_NO_NODE. Also, skip the lookup if @node is
online. This makes the routine compatible with other arch node mapping
routines.
Reported-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Reviewed-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Link: https://lore.kernel.org/r/157401275716.43284.13185549705765009174.stgit@dwillia2-desk3.amr.corp.intel.comReviewed-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Link: https://lore.kernel.org/r/158188325316.894464.15650888748083329531.stgit@dwillia2-desk3.amr.corp.intel.com

mm/mempolicy.c

@@ -135,15 +135,12 @@ static struct mempolicy preferred_node_policy[MAX_NUMNODES];
  */
 int numa_map_to_online_node(int node)
 {
-	int min_node;
+	int min_dist = INT_MAX, dist, n, min_node;
 
-	if (node == NUMA_NO_NODE)
-		node = 0;
+	if (node == NUMA_NO_NODE || node_online(node))
+		return node;
 
 	min_node = node;
-	if (!node_online(node)) {
-		int min_dist = INT_MAX, dist, n;
-
 	for_each_online_node(n) {
 		dist = node_distance(node, n);
 		if (dist < min_dist) {
@@ -151,7 +148,6 @@ int numa_map_to_online_node(int node)
 			min_node = n;
 		}
 	}
-	}
 
 	return min_node;
 }