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 @@ -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; _
