mm: bdi init hooks

provide BDI constructor/destructor hooks

[akpm@linux-foundation.org: compile fix]
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
diff --git a/mm/swap.c b/mm/swap.c
index d034b21..a65eff8 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -28,6 +28,7 @@
 #include <linux/percpu.h>
 #include <linux/cpu.h>
 #include <linux/notifier.h>
+#include <linux/backing-dev.h>
 
 /* How many pages do we try to swap or page in/out together? */
 int page_cluster;
@@ -547,6 +548,10 @@
 {
 	unsigned long megs = num_physpages >> (20 - PAGE_SHIFT);
 
+#ifdef CONFIG_SWAP
+	bdi_init(swapper_space.backing_dev_info);
+#endif
+
 	/* Use a smaller cluster for small-memory machines */
 	if (megs < 16)
 		page_cluster = 2;