The patch titled
Subject: mm/page_alloc: add penalty to local_node
has been added to the -mm tree. Its filename is
mm-page_alloc-add-penalty-to-local_node.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-page_alloc-add-penalty-to-local_node.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-page_alloc-add-penalty-to-local_node.patch
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------------------------------------------------------
From: Wei Yang <richard.weiyang@xxxxxxxxx>
Subject: mm/page_alloc: add penalty to local_node
Commit 54d032ced983 ("mm/page_alloc: use accumulated load when building
node fallback list") fixed a bug on zonelist order. This made me think
about what would happen if we have a node system with the following
distance matrix.
Node 0 1 2 3 4 5 6 7
----------------------------
0 10 12 12 12 32 32 32 32
1 12 10 12 12 32 32 32 32
2 12 12 10 12 32 32 32 32
3 12 12 12 10 32 32 32 32
4 32 32 32 32 10 12 12 12
5 32 32 32 32 12 10 12 12
6 32 32 32 32 12 12 10 12
7 32 32 32 32 12 12 12 10
Unfortunately for this case, the node fallback list gets built like this:
Node Fallback list
---------------------
0: 0 1 2 3 4 5 6 7
1: 1 0 2 3 5 6 7 4
2: 2 3 0 1 6 7 4 5
3: 3 2 0 1 7 4 5 6
4: 4 5 6 7 0 1 2 3
5: 5 4 6 7 1 2 3 0
6: 6 7 4 5 2 3 0 1
7: 7 6 4 5 3 0 1 2
We found the order in diagonal block is not expected. The reason is we
don't penaltize local node.
After penalizing local node, the node fallback list gets built like this:
Node Fallback list
---------------------
0: 0 1 2 3 4 5 6 7
1: 1 2 3 0 5 6 7 4
2: 2 3 0 1 6 7 4 5
3: 3 0 1 2 7 4 5 6
4: 4 5 6 7 0 1 2 3
5: 5 6 7 4 1 2 3 0
6: 6 7 4 5 2 3 0 1
7: 7 4 5 6 3 0 1 2
Now the fallback list is in round-robin order.
I am not very familiar with the node distance pattern, while I tried the
following distance matrix. Both of them works with this change.
Node 0 1 2 3
----------------
0 10 10 10 10
1 10 10 10 10
2 10 10 10 10
3 10 10 10 10
Node 0 1 2 3 4 5 6 7
----------------------------
0 10 10 10 10 32 32 32 32
1 10 10 10 10 32 32 32 32
2 10 10 10 10 32 32 32 32
3 10 10 10 10 32 32 32 32
4 32 32 32 32 10 10 10 10
5 32 32 32 32 10 10 10 10
6 32 32 32 32 10 10 10 10
7 32 32 32 32 10 10 10 10
Link: https://lkml.kernel.org/r/20220123013537.20491-2-richard.weiyang@xxxxxxxxx
Signed-off-by: Wei Yang <richard.weiyang@xxxxxxxxx>
Cc: Krupa Ramakrishnan <krupa.ramakrishnan@xxxxxxx>
Cc: KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)
--- a/mm/page_alloc.c~mm-page_alloc-add-penalty-to-local_node
+++ a/mm/page_alloc.c
@@ -6334,8 +6334,9 @@ static void build_zonelists(pg_data_t *p
* So adding penalty to the first node in same
* distance group to make it round-robin.
*/
- if (node_distance(local_node, node) !=
- node_distance(local_node, prev_node))
+ if ((node_distance(local_node, node) !=
+ node_distance(local_node, prev_node)) ||
+ node == local_node)
node_load[node] += nr_online_nodes;
node_order[nr_nodes++] = node;
_
Patches currently in -mm which might be from richard.weiyang@xxxxxxxxx are
mm-page-mapping-folio-mapping-should-have-the-same-offset.patch
mm-page_alloc-add-same-penalty-is-enough-to-get-round-robin-order.patch
mm-page_alloc-add-penalty-to-local_node.patch
