[Pmem] [PATCH 16/17] mm: migrate: add more comments for selecting target node randomly

commit f108f1956ecbcd9c6190e0c75bc2c96cda9289c4 upstream 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+g7dfzeOw8fPyeEC0BBv13Ny1UVGHDkadnQ… Link: https://lkml.kernel.org/r/c31d36bd097c6e9e69fc0f409c43b78e53e64fc2.16377668… Signed-off-by: Baolin Wang <baolin.wang(a)linux.alibaba.com> Reviewed-by: Yang Shi <shy828301(a)gmail.com> Cc: "Huang, Ying" <ying.huang(a)intel.com> Cc: Dave Hansen <dave.hansen(a)linux.intel.com> Cc: Zi Yan <ziy(a)nvidia.com> Cc: zhongjiang-ali <zhongjiang-ali(a)linux.alibaba.com> Cc: Xunlei Pang <xlpang(a)linux.alibaba.com> Signed-off-by: Andrew Morton <akpm(a)linux-foundation.org> Signed-off-by: Mark Brown <broonie(a)kernel.org> --- mm/migrate.c | 8 ++++++++ 1 file changed, 8 insertions(+) diff --git a/mm/migrate.c b/mm/migrate.c index 10c14d1..bd3d656 100644 --- a/mm/migrate.c +++ b/mm/migrate.c @@ -1268,6 +1268,14 @@ 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; -- 1.8.3.1