[PATCH] mm: Untangle config dependencies for demote-on-reclaim

[Oscar Salvador <osalvador@xxxxxxx>]

At the time demote-on-reclaim was introduced, it was tied to
CONFIG_HOTPLUG_CPU + CONFIG_MIGRATE, but that is not really
accurate.

The only two things we need to depen on is CONFIG_NUMA +
CONFIG_MIGRATE, so clean this up.
Furthermore, we only register the hotplug memory notifier
when the system has CONFIG_MEMORY_HOTPLUG.

Signed-off-by: Oscar Salvador <osalvador@xxxxxxx>
Suggested-by: "Huang, Ying" <ying.huang@xxxxxxxxx>
---
 include/linux/migrate.h |  5 ++++-
 mm/migrate.c            | 11 ++++++-----
 mm/vmstat.c             |  2 --
 3 files changed, 10 insertions(+), 8 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a4a336fd81fc..1efabe7bb5fc 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -49,14 +49,17 @@ int folio_migrate_mapping(struct address_space *mapping,
 
 extern bool numa_demotion_enabled;
 extern void migrate_on_reclaim_init(void);
-#ifdef CONFIG_HOTPLUG_CPU
+#ifdef CONFIG_NUMA
 extern void set_migration_target_nodes(void);
+extern void migrate_on_reclaim_init(void);
 #else
 static inline void set_migration_target_nodes(void) {}
+static inline void migrate_on_reclaim_init(void) {}
 #endif
 #else
 
 static inline void set_migration_target_nodes(void) {}
+static inline void migrate_on_reclaim_init(void) {}
 
 static inline void putback_movable_pages(struct list_head *l) {}
 static inline int migrate_pages(struct list_head *l, new_page_t new,
diff --git a/mm/migrate.c b/mm/migrate.c
index 3364bfaddeef..118f71425241 100644
--- a/mm/migrate.c
+++ b/mm/migrate.c
@@ -2144,7 +2144,6 @@ int migrate_misplaced_page(struct page *page, struct vm_area_struct *vma,
 	return 0;
 }
 #endif /* CONFIG_NUMA_BALANCING */
-#endif /* CONFIG_NUMA */
 
 /*
  * node_demotion[] example:
@@ -2278,7 +2277,6 @@ int next_demotion_node(int node)
 	return target;
 }
 
-#if defined(CONFIG_HOTPLUG_CPU)
 /* Disable reclaim-based migration. */
 static void __disable_all_migrate_targets(void)
 {
@@ -2471,6 +2469,7 @@ void set_migration_target_nodes(void)
  * __set_migration_target_nodes() can be used as opposed to
  * set_migration_target_nodes().
  */
+#ifdef CONFIG_MEMORY_HOTPLUG
 static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
 						 unsigned long action, void *_arg)
 {
@@ -2516,6 +2515,7 @@ static int __meminit migrate_on_reclaim_callback(struct notifier_block *self,
 
 	return notifier_from_errno(0);
 }
+#endif
 
 void __init migrate_on_reclaim_init(void)
 {
@@ -2523,8 +2523,9 @@ void __init migrate_on_reclaim_init(void)
 				      sizeof(struct demotion_nodes),
 				      GFP_KERNEL);
 	WARN_ON(!node_demotion);
-
+#ifdef CONFIG_MEMORY_HOTPLUG
 	hotplug_memory_notifier(migrate_on_reclaim_callback, 100);
+#endif
 	/*
 	 * At this point, all numa nodes with memory/CPus have their state
 	 * properly set, so we can build the demotion order now.
@@ -2535,7 +2536,6 @@ void __init migrate_on_reclaim_init(void)
 	set_migration_target_nodes();
 	cpus_read_unlock();
 }
-#endif /* CONFIG_HOTPLUG_CPU */
 
 bool numa_demotion_enabled = false;
 
@@ -2596,4 +2596,5 @@ static int __init numa_init_sysfs(void)
 	return err;
 }
 subsys_initcall(numa_init_sysfs);
-#endif
+#endif /* CONFIG_SYSFS */
+#endif /* CONFIG_NUMA */
diff --git a/mm/vmstat.c b/mm/vmstat.c
index b75b1a64b54c..f2d0dec1062d 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -2111,9 +2111,7 @@ void __init init_mm_internals(void)
 
 	start_shepherd_timer();
 #endif
-#if defined(CONFIG_MIGRATION) && defined(CONFIG_HOTPLUG_CPU)
 	migrate_on_reclaim_init();
-#endif
 #ifdef CONFIG_PROC_FS
 	proc_create_seq("buddyinfo", 0444, NULL, &fragmentation_op);
 	proc_create_seq("pagetypeinfo", 0400, NULL, &pagetypeinfo_op);
-- 
2.34.1