[RFC][PATCH v2 09/21] mm: avoid duplicate peer target node

[Fengguang Wu]

To ensure 1:1 peer node mapping on broken BIOS

	node distances:
	node   0   1   2   3
	  0:  10  21  20  20
	  1:  21  10  20  20
	  2:  20  20  10  20
	  3:  20  20  20  10

or with numa=fake=4U

	node distances:
	node   0   1   2   3   4   5   6   7   8   9  10  11  12  13  14  15
	  0:  10  10  10  10  21  21  21  21  17  17  17  17  28  28  28  28
	  1:  10  10  10  10  21  21  21  21  17  17  17  17  28  28  28  28
	  2:  10  10  10  10  21  21  21  21  17  17  17  17  28  28  28  28
	  3:  10  10  10  10  21  21  21  21  17  17  17  17  28  28  28  28
	  4:  21  21  21  21  10  10  10  10  28  28  28  28  17  17  17  17
	  5:  21  21  21  21  10  10  10  10  28  28  28  28  17  17  17  17
	  6:  21  21  21  21  10  10  10  10  28  28  28  28  17  17  17  17
	  7:  21  21  21  21  10  10  10  10  28  28  28  28  17  17  17  17
	  8:  17  17  17  17  28  28  28  28  10  10  10  10  28  28  28  28
	  9:  17  17  17  17  28  28  28  28  10  10  10  10  28  28  28  28
	 10:  17  17  17  17  28  28  28  28  10  10  10  10  28  28  28  28
	 11:  17  17  17  17  28  28  28  28  10  10  10  10  28  28  28  28
	 12:  28  28  28  28  17  17  17  17  28  28  28  28  10  10  10  10
	 13:  28  28  28  28  17  17  17  17  28  28  28  28  10  10  10  10
	 14:  28  28  28  28  17  17  17  17  28  28  28  28  10  10  10  10
	 15:  28  28  28  28  17  17  17  17  28  28  28  28  10  10  10  10

Signed-off-by: Fengguang Wu <fengguang.wu@xxxxxxxxx>
---
 mm/page_alloc.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- linux.orig/mm/page_alloc.c	2018-12-23 19:48:27.366110325 +0800
+++ linux/mm/page_alloc.c	2018-12-23 19:48:27.362110332 +0800
@@ -6941,16 +6941,22 @@ static int find_best_peer_node(int nid)
 	int n, val;
 	int min_val = INT_MAX;
 	int peer = NUMA_NO_NODE;
+	static nodemask_t target_nodes = NODE_MASK_NONE;
 
 	for_each_online_node(n) {
 		if (n == nid)
 			continue;
 		val = node_distance(nid, n);
+		if (val == LOCAL_DISTANCE)
+			continue;
+		if (node_isset(n, target_nodes))
+			continue;
 		if (val < min_val) {
 			min_val = val;
 			peer = n;
 		}
 	}
+	node_set(peer, target_nodes);
 	return peer;
 }