[PATCH 2/2] mm/migrate: add CPU hotplug to demotion #ifdef

[Dave Hansen]

From: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>

Once upon a time, the node demotion updates were driven solely by
memory hotplug events.  But now, there are  handlers for both CPU
and memory hotplug.

However, the #ifdef around the code checks only memory hotplug.
A system that has HOTPLUG_CPU=y but MEMORY_HOTPLUG=n would miss
CPU hotplug events.

Update the #ifdef around the common code.  Add memory and
CPU-specific #ifdefs for their handlers.  These memory/CPU
#ifdefs avoid unused function warnings when their Kconfig option
is off.

Fixes: 884a6e5d1f93 ("mm/migrate: update node demotion order on hotplug events")
Signed-off-by: Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx>
Cc: "Huang, Ying" <ying.huang@xxxxxxxxx>
Cc: Michal Hocko <mhocko@xxxxxxxx>
Cc: Wei Xu <weixugc@xxxxxxxxxx>
Cc: Oscar Salvador <osalvador@xxxxxxx>
Cc: David Rientjes <rientjes@xxxxxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: Greg Thelen <gthelen@xxxxxxxxxx>
Cc: Yang Shi <yang.shi@xxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 b/mm/migrate.c |   46 +++++++++++++++++++++++++---------------------
 1 file changed, 25 insertions(+), 21 deletions(-)

diff -puN mm/migrate.c~add-cpu-hotplug-config mm/migrate.c
--- a/mm/migrate.c~add-cpu-hotplug-config	2021-09-24 09:12:31.308377810 -0700
+++ b/mm/migrate.c	2021-09-24 09:12:31.308377810 -0700
@@ -3066,7 +3066,7 @@ void migrate_vma_finalize(struct migrate
 EXPORT_SYMBOL(migrate_vma_finalize);
 #endif /* CONFIG_DEVICE_PRIVATE */
 
-#if defined(CONFIG_MEMORY_HOTPLUG)
+#if defined(CONFIG_MEMORY_HOTPLUG) || defined(CONFIG_HOTPLUG_CPU)
 /* Disable reclaim-based migration. */
 static void __disable_all_migrate_targets(void)
 {
@@ -3208,25 +3208,7 @@ static void set_migration_target_nodes(v
 	put_online_mems();
 }
 
-/*
- * React to hotplug events that might affect the migration targets
- * like events that online or offline NUMA nodes.
- *
- * 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)
-{
-	set_migration_target_nodes();
-	return 0;
-}
-
-static int migration_offline_cpu(unsigned int cpu)
-{
-	set_migration_target_nodes();
-	return 0;
-}
-
+#if defined(CONFIG_MEMORY_HOTPLUG)
 /*
  * This leaves migrate-on-reclaim transiently disabled between
  * the MEM_GOING_OFFLINE and MEM_OFFLINE events.  This runs
@@ -3283,6 +3265,27 @@ static int __meminit migrate_on_reclaim_
 
 	return notifier_from_errno(0);
 }
+#endif /* CONFIG_MEMORY_HOTPLUG */
+
+#ifdef CONFIG_HOTPLUG_CPU
+/*
+ * React to hotplug events that might affect the migration targets
+ * like events that online or offline NUMA nodes.
+ *
+ * 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)
+{
+	set_migration_target_nodes();
+	return 0;
+}
+
+static int migration_offline_cpu(unsigned int cpu)
+{
+	set_migration_target_nodes();
+	return 0;
+}
 
 static int __init migrate_on_reclaim_init(void)
 {
@@ -3303,4 +3306,5 @@ static int __init migrate_on_reclaim_ini
 	return 0;
 }
 late_initcall(migrate_on_reclaim_init);
-#endif /* CONFIG_MEMORY_HOTPLUG */
+#endif /* CONFIG_HOTPLUG_CPU */
+#endif /* CONFIG_MEMORY_HOTPLUG || CONFIG_HOTPLUG_CPU */
_