[PATCH v2] 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>
---
v1 -> v2: Feedback from "Huang, Ying"
---
 include/linux/migrate.h | 34 +++++++++++++++-------------------
 mm/migrate.c            | 11 ++++++-----
 mm/vmstat.c             |  2 --
 3 files changed, 21 insertions(+), 26 deletions(-)

diff --git a/include/linux/migrate.h b/include/linux/migrate.h
index a4a336fd81fc..97407596f058 100644
--- a/include/linux/migrate.h
+++ b/include/linux/migrate.h
@@ -47,17 +47,8 @@ void folio_migrate_copy(struct folio *newfolio, struct folio *folio);
 int folio_migrate_mapping(struct address_space *mapping,
 		struct folio *newfolio, struct folio *folio, int extra_count);
 
-extern bool numa_demotion_enabled;
-extern void migrate_on_reclaim_init(void);
-#ifdef CONFIG_HOTPLUG_CPU
-extern void set_migration_target_nodes(void);
-#else
-static inline void set_migration_target_nodes(void) {}
-#endif
 #else
 
-static inline void set_migration_target_nodes(void) {}
-
 static inline void putback_movable_pages(struct list_head *l) {}
 static inline int migrate_pages(struct list_head *l, new_page_t new,
 		free_page_t free, unsigned long private, enum migrate_mode mode,
@@ -82,9 +73,23 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 	return -ENOSYS;
 }
 
-#define numa_demotion_enabled	false
 #endif /* CONFIG_MIGRATION */
 
+#if defined(CONFIG_MIGRATION) && defined(CONFIG_NUMA)
+extern void set_migration_target_nodes(void);
+extern void migrate_on_reclaim_init(void);
+extern bool numa_demotion_enabled;
+extern int next_demotion_node(int node);
+#else
+static inline void set_migration_target_nodes(void) {}
+static inline void migrate_on_reclaim_init(void) {}
+static inline int next_demotion_node(int node)
+{
+        return NUMA_NO_NODE;
+}
+#define numa_demotion_enabled  false
+#endif
+
 #ifdef CONFIG_COMPACTION
 extern int PageMovable(struct page *page);
 extern void __SetPageMovable(struct page *page, struct address_space *mapping);
@@ -173,15 +178,6 @@ struct migrate_vma {
 int migrate_vma_setup(struct migrate_vma *args);
 void migrate_vma_pages(struct migrate_vma *migrate);
 void migrate_vma_finalize(struct migrate_vma *migrate);
-int next_demotion_node(int node);
-
-#else /* CONFIG_MIGRATION disabled: */
-
-static inline int next_demotion_node(int node)
-{
-	return NUMA_NO_NODE;
-}
-
 #endif /* CONFIG_MIGRATION */
 
 #endif /* _LINUX_MIGRATE_H */
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