The patch titled
Subject: mm: migrate: add more comments for selecting target node randomly
has been added to the -mm tree. Its filename is
mm-migrate-add-more-comments-for-selecting-target-node-randomly.patch
This patch should soon appear at
https://ozlabs.org/~akpm/mmots/broken-out/mm-migrate-add-more-comments-for-selecting-target-node-randomly.patch
and later at
https://ozlabs.org/~akpm/mmotm/broken-out/mm-migrate-add-more-comments-for-selecting-target-node-randomly.patch
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------------------------------------------------------
From: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Subject: mm: migrate: add more comments for selecting target node randomly
As Yang Shi suggested [1], it will be helpful to explain why we should
select target node randomly now if there are multiple target nodes.
[1] https://lore.kernel.org/all/CAHbLzkqSqCL+g7dfzeOw8fPyeEC0BBv13Ny1UVGHDkadnQdR=g@xxxxxxxxxxxxxx/
Link: https://lkml.kernel.org/r/c31d36bd097c6e9e69fc0f409c43b78e53e64fc2.1637766801.git.baolin.wang@xxxxxxxxxxxxxxxxx
Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
Reviewed-by: Yang Shi <shy828301@xxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: Zi Yan <ziy@xxxxxxxxxx>
Cc: zhongjiang-ali <zhongjiang-ali@xxxxxxxxxxxxxxxxx>
Cc: Xunlei Pang <xlpang@xxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/migrate.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/mm/migrate.c~mm-migrate-add-more-comments-for-selecting-target-node-randomly
+++ a/mm/migrate.c
@@ -1196,6 +1196,14 @@ int next_demotion_node(int node)
/*
* If there are multiple target nodes, just select one
* target node randomly.
+ *
+ * In addition, we can also use round-robin to select
+ * target node, but we should introduce another variable
+ * for node_demotion[] to record last selected target node,
+ * that may cause cache ping-pong due to the changing of
+ * last target node. Or introducing per-cpu data to avoid
+ * caching issue, which seems more complicated. So selecting
+ * target node randomly seems better until now.
*/
index = get_random_int() % target_nr;
break;
_
Patches currently in -mm which might be from baolin.wang@xxxxxxxxxxxxxxxxx are
mm-migrate-fix-the-return-value-of-migrate_pages.patch
mm-migrate-correct-the-hugetlb-migration-stats.patch
mm-compaction-fix-the-migration-stats-in-trace_mm_compaction_migratepages.patch
mm-migrate-support-multiple-target-nodes-demotion.patch
mm-migrate-add-more-comments-for-selecting-target-node-randomly.patch
