From: Baolin Wang <baolin.wang@linux.alibaba.com>
Date: Fri, 14 Jan 2022 14:08:46 -0800
Subject: mm: migrate: add more comments for selecting target node randomly
Git-commit: 7813a1b5257b8eb2cb915cd08e7ba857070fdfd3
Patch-mainline: v5.17-rc1
References: jsc#PED-1247
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/
Link: https://lkml.kernel.org/r/c31d36bd097c6e9e69fc0f409c43b78e53e64fc2.1637766801.git.baolin.wang@linux.alibaba.com
Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Yang Shi <shy828301@gmail.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Cc: Zi Yan <ziy@nvidia.com>
Cc: zhongjiang-ali <zhongjiang-ali@linux.alibaba.com>
Cc: Xunlei Pang <xlpang@linux.alibaba.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
---
mm/migrate.c | 8 ++++++++
1 file changed, 8 insertions(+)
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -1214,6 +1214,14 @@ 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;