[PATCH] Handle holes in node mask in node fallback list setup

Change the find_next_best_node algorithm to correctly skip
over holes in the node online mask. Previously it would not handle
missing nodes correctly and cause crashes at boot.

[Written by Linus, tested by AK]

Signed-off-by: Andi Kleen <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

mm/page_alloc.c

···
  */
 static int __init find_next_best_node(int node, nodemask_t *used_node_mask)
 {
-	int i, n, val;
+	int n, val;
 	int min_val = INT_MAX;
 	int best_node = -1;
 
-	for_each_online_node(i) {
-		cpumask_t tmp;
+	/* Use the local node if we haven't already */
+	if (!node_isset(node, *used_node_mask)) {
+		node_set(node, *used_node_mask);
+		return node;
+	}
 
-		/* Start from local node */
-		n = (node+i) % num_online_nodes();
+	for_each_online_node(n) {
+		cpumask_t tmp;
 
 		/* Don't want a node to appear more than once */
 		if (node_isset(n, *used_node_mask))
 			continue;
 
-		/* Use the local node if we haven't already */
-		if (!node_isset(node, *used_node_mask)) {
-			best_node = node;
-			break;
-		}
-
 		/* Use the distance array to find the distance */
 		val = node_distance(node, n);
+
+		/* Penalize nodes under us ("prefer the next node") */
+		val += (n < node);
 
 		/* Give preference to headless and unused nodes */
 		tmp = node_to_cpumask(n);