mm: migrate: make demotion knob depend on migration

The memory demotion needs to call migrate_pages() to do the jobs.  And
it is controlled by a knob, however, the knob doesn't depend on
CONFIG_MIGRATION.  The knob could be truned on even though MIGRATION is
disabled, this will not cause any crash since migrate_pages() would just
return -ENOSYS.  But it is definitely not optimal to go through demotion
path then retry regular swap every time.

And it doesn't make too much sense to have the knob visible to the users
when !MIGRATION.  Move the related code from mempolicy.[h|c] to
migrate.[h|c].

Link: https://lkml.kernel.org/r/20211015005559.246709-1-shy828301@gmail.comSigned-off-by: Yang Shi <shy828301@gmail.com>
Acked-by: "Huang, Ying" <ying.huang@intel.com>
Cc: Dave Hansen <dave.hansen@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mempolicy.h

@@ -183,8 +183,6 @@ extern bool vma_migratable(struct vm_area_struct *vma);
 extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
 extern void mpol_put_task_policy(struct task_struct *);
 
-extern bool numa_demotion_enabled;
-
 static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 {
 	return  (pol->mode == MPOL_PREFERRED_MANY);
@@ -300,8 +298,6 @@ static inline nodemask_t *policy_nodemask_current(gfp_t gfp)
 	return NULL;
 }
 
-#define numa_demotion_enabled	false
-
 static inline bool mpol_is_preferred_many(struct mempolicy *pol)
 {
 	return  false;

include/linux/migrate.h

@@ -40,6 +40,8 @@ extern int migrate_huge_page_move_mapping(struct address_space *mapping,
 				  struct page *newpage, struct page *page);
 extern int migrate_page_move_mapping(struct address_space *mapping,
 		struct page *newpage, struct page *page, int extra_count);
+
+extern bool numa_demotion_enabled;
 #else
 
 static inline void putback_movable_pages(struct list_head *l) {}
@@ -65,6 +67,8 @@ static inline int migrate_huge_page_move_mapping(struct address_space *mapping,
 {
 	return -ENOSYS;
 }
+
+#define numa_demotion_enabled	false
 #endif /* CONFIG_MIGRATION */
 
 #ifdef CONFIG_COMPACTION

mm/mempolicy.c

@@ -3057,64 +3057,3 @@ void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol)
 		p += scnprintf(p, buffer + maxlen - p, ":%*pbl",
 			       nodemask_pr_args(&nodes));
 }
-
-bool numa_demotion_enabled = false;
-
-#ifdef CONFIG_SYSFS
-static ssize_t numa_demotion_enabled_show(struct kobject *kobj,
-					  struct kobj_attribute *attr, char *buf)
-{
-	return sysfs_emit(buf, "%s\n",
-			  numa_demotion_enabled? "true" : "false");
-}
-
-static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
-					   struct kobj_attribute *attr,
-					   const char *buf, size_t count)
-{
-	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
-		numa_demotion_enabled = true;
-	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
-		numa_demotion_enabled = false;
-	else
-		return -EINVAL;
-
-	return count;
-}
-
-static struct kobj_attribute numa_demotion_enabled_attr =
-	__ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
-	       numa_demotion_enabled_store);
-
-static struct attribute *numa_attrs[] = {
-	&numa_demotion_enabled_attr.attr,
-	NULL,
-};
-
-static const struct attribute_group numa_attr_group = {
-	.attrs = numa_attrs,
-};
-
-static int __init numa_init_sysfs(void)
-{
-	int err;
-	struct kobject *numa_kobj;
-
-	numa_kobj = kobject_create_and_add("numa", mm_kobj);
-	if (!numa_kobj) {
-		pr_err("failed to create numa kobject\n");
-		return -ENOMEM;
-	}
-	err = sysfs_create_group(numa_kobj, &numa_attr_group);
-	if (err) {
-		pr_err("failed to register numa group\n");
-		goto delete_obj;
-	}
-	return 0;
-
-delete_obj:
-	kobject_put(numa_kobj);
-	return err;
-}
-subsys_initcall(numa_init_sysfs);
-#endif

mm/migrate.c

@@ -3306,3 +3306,64 @@ static int __init migrate_on_reclaim_init(void)
 }
 late_initcall(migrate_on_reclaim_init);
 #endif /* CONFIG_HOTPLUG_CPU */
+
+bool numa_demotion_enabled = false;
+
+#ifdef CONFIG_SYSFS
+static ssize_t numa_demotion_enabled_show(struct kobject *kobj,
+					  struct kobj_attribute *attr, char *buf)
+{
+	return sysfs_emit(buf, "%s\n",
+			  numa_demotion_enabled ? "true" : "false");
+}
+
+static ssize_t numa_demotion_enabled_store(struct kobject *kobj,
+					   struct kobj_attribute *attr,
+					   const char *buf, size_t count)
+{
+	if (!strncmp(buf, "true", 4) || !strncmp(buf, "1", 1))
+		numa_demotion_enabled = true;
+	else if (!strncmp(buf, "false", 5) || !strncmp(buf, "0", 1))
+		numa_demotion_enabled = false;
+	else
+		return -EINVAL;
+
+	return count;
+}
+
+static struct kobj_attribute numa_demotion_enabled_attr =
+	__ATTR(demotion_enabled, 0644, numa_demotion_enabled_show,
+	       numa_demotion_enabled_store);
+
+static struct attribute *numa_attrs[] = {
+	&numa_demotion_enabled_attr.attr,
+	NULL,
+};
+
+static const struct attribute_group numa_attr_group = {
+	.attrs = numa_attrs,
+};
+
+static int __init numa_init_sysfs(void)
+{
+	int err;
+	struct kobject *numa_kobj;
+
+	numa_kobj = kobject_create_and_add("numa", mm_kobj);
+	if (!numa_kobj) {
+		pr_err("failed to create numa kobject\n");
+		return -ENOMEM;
+	}
+	err = sysfs_create_group(numa_kobj, &numa_attr_group);
+	if (err) {
+		pr_err("failed to register numa group\n");
+		goto delete_obj;
+	}
+	return 0;
+
+delete_obj:
+	kobject_put(numa_kobj);
+	return err;
+}
+subsys_initcall(numa_init_sysfs);
+#endif