ceph: enable readahead

Initialized bdi->ra_pages to enable readahead.  Use 512KB default.

Signed-off-by: Sage Weil <sage@newdream.net>
diff --git a/fs/ceph/super.h b/fs/ceph/super.h
index 0bbf58a..75556e9 100644
--- a/fs/ceph/super.h
+++ b/fs/ceph/super.h
@@ -69,7 +69,7 @@
  * defaults
  */
 #define CEPH_MOUNT_TIMEOUT_DEFAULT  60
-#define CEPH_MOUNT_RSIZE_DEFAULT    (128*1024) /* readahead */
+#define CEPH_MOUNT_RSIZE_DEFAULT    (512*1024) /* readahead */
 
 #define CEPH_MSG_MAX_FRONT_LEN	(16*1024*1024)
 #define CEPH_MSG_MAX_DATA_LEN	(16*1024*1024)