[PATCH] mm/migrate: Debug CPU hotplug regression

[Huang Ying <ying.huang@xxxxxxxxx>]

Signed-off-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
 mm/migrate.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/mm/migrate.c b/mm/migrate.c
index c7da064b4781..c4805f15e616 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -3261,15 +3261,17 @@ static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
  * The ordering is also currently dependent on which nodes have
  * CPUs.  That means we need CPU on/offline notification too.
  */
-static int migration_online_cpu(unsigned int cpu)
+static int migration_cpu_hotplug(unsigned int cpu)
 {
-	set_migration_target_nodes();
-	return 0;
-}
+	static int nr_cpu_node_saved;
+	int nr_cpu_node;
+
+	nr_cpu_node = num_node_state(N_CPU);
+	if (nr_cpu_node != nr_cpu_node_saved) {
+		set_migration_target_nodes();
+		nr_cpu_node_saved = nr_cpu_node;
+	}
 
-static int migration_offline_cpu(unsigned int cpu)
-{
-	set_migration_target_nodes();
 	return 0;
 }
 
@@ -3283,7 +3285,7 @@ static int __init migrate_on_reclaim_init(void)
 	WARN_ON(!node_demotion);
 
 	ret = cpuhp_setup_state_nocalls(CPUHP_MM_DEMOTION_DEAD, "mm/demotion:offline",
-					NULL, migration_offline_cpu);
+					NULL, migration_cpu_hotplug);
 	/*
 	 * In the unlikely case that this fails, the automatic
 	 * migration targets may become suboptimal for nodes
@@ -3292,7 +3294,7 @@ static int __init migrate_on_reclaim_init(void)
 	 */
 	WARN_ON(ret < 0);
 	ret = cpuhp_setup_state(CPUHP_AP_MM_DEMOTION_ONLINE, "mm/demotion:online",
-				migration_online_cpu, NULL);
+				migration_cpu_hotplug, NULL);
 	WARN_ON(ret < 0);
 
 	hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
-- 
2.30.2