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Subject[PATCH] mm: migrate: Add more comments for selecting target node randomly
Date
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@mail.gmail.com/
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
mm/migrate.c | 8 ++++++++
1 file changed, 8 insertions(+)

diff --git a/mm/migrate.c b/mm/migrate.c
index 8d39720de4eb..d9af89248196 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1209,6 +1209,14 @@ 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;
--
2.27.0
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