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Subject[RFC][PATCH v2 09/21] mm: avoid duplicate peer target node
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@intel.com>
---
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;
}


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