mm: only build per-node scan_unevictable functions when NUMA is enabled

Non-NUMA systems do never create these files anyway, since they are only
created by driver subsystem when NUMA is configured.

[akpm@linux-foundation.org: cleanup]
Signed-off-by: NThadeu Lima de Souza Cascardo <cascardo@holoscopio.com>
Reviewed-by: NKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: Lee Schermerhorn <lee.schermerhorn@hp.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

include/linux/swap.h

@@ -271,8 +271,18 @@ extern void scan_mapping_unevictable_pages(struct address_space *);
 extern unsigned long scan_unevictable_pages;
 extern int scan_unevictable_handler(struct ctl_table *, int,
 					void __user *, size_t *, loff_t *);
+#ifdef CONFIG_NUMA
 extern int scan_unevictable_register_node(struct node *node);
 extern void scan_unevictable_unregister_node(struct node *node);
+#else
+static inline int scan_unevictable_register_node(struct node *node)
+{
+	return 0;
+}
+static inline void scan_unevictable_unregister_node(struct node *node)
+{
+}
+#endif
 
 extern int kswapd_run(int nid);
 extern void kswapd_stop(int nid);

mm/vmscan.c

@@ -2986,6 +2986,7 @@ int scan_unevictable_handler(struct ctl_table *table, int write,
 	return 0;
 }
 
+#ifdef CONFIG_NUMA
 /*
  * per node 'scan_unevictable_pages' attribute.  On demand re-scan of
  * a specified node's per zone unevictable lists for evictable pages.
@@ -3032,4 +3033,4 @@ void scan_unevictable_unregister_node(struct node *node)
 {
 	sysdev_remove_file(&node->sysdev, &attr_scan_unevictable_pages);
 }
-
+#endif