mm: cleancache: clean up cleancache_enabled

cleancache_ops is used to decide whether backend is registered.
So now cleancache_enabled is always true if defined CONFIG_CLEANCACHE.

Signed-off-by: Bob Liu <[email protected]>
Cc: Wanpeng Li <[email protected]>
Cc: Andor Daam <[email protected]>
Cc: Dan Magenheimer <[email protected]>
Cc: Florian Schmaus <[email protected]>
Cc: Konrad Rzeszutek Wilk <[email protected]>
Cc: Minchan Kim <[email protected]>
Cc: Stefan Hengelein <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
diff --git a/include/linux/cleancache.h b/include/linux/cleancache.h
index 3af5ea8..4ce9056b 100644
--- a/include/linux/cleancache.h
+++ b/include/linux/cleancache.h
@@ -42,9 +42,9 @@
 extern void __cleancache_invalidate_page(struct address_space *, struct page *);
 extern void __cleancache_invalidate_inode(struct address_space *);
 extern void __cleancache_invalidate_fs(struct super_block *);
-extern int cleancache_enabled;
 
 #ifdef CONFIG_CLEANCACHE
+#define cleancache_enabled (1)
 static inline bool cleancache_fs_enabled(struct page *page)
 {
 	return page->mapping->host->i_sb->cleancache_poolid >= 0;