From 7813a1b5257b8eb2cb915cd08e7ba857070fdfd3 Mon Sep 17 00:00:00 2001 From: Baolin Wang Date: Fri, 14 Jan 2022 14:08:46 -0800 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@mail.gmail.com/ Link: https://lkml.kernel.org/r/c31d36bd097c6e9e69fc0f409c43b78e53e64fc2.1637766801.git.baolin.wang@linux.alibaba.com Signed-off-by: Baolin Wang Reviewed-by: Yang Shi Cc: "Huang, Ying" Cc: Dave Hansen Cc: Zi Yan Cc: zhongjiang-ali Cc: Xunlei Pang Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- mm/migrate.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index 9d2642a34018..f50087d3ebf2 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1206,6 +1206,14 @@ 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; -- cgit v1.2.3