Index: linux-2.6/fs/fs-writeback.c
===================================================================
--- linux-2.6.orig/fs/fs-writeback.c	2010-11-23 20:57:23.000000000 +1100
+++ linux-2.6/fs/fs-writeback.c	2010-11-23 20:59:10.000000000 +1100
@@ -1152,16 +1152,17 @@ EXPORT_SYMBOL(writeback_inodes_sb);
  *
  * Invoke writeback_inodes_sb if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
+ *
+ * Even if 1 is returned, writeback may not be started if memory allocation
+ * fails. This function makes no guarantees about anything.
  */
 int writeback_inodes_sb_if_idle(struct super_block *sb)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
-		down_read(&sb->s_umount);
-		writeback_inodes_sb(sb);
-		up_read(&sb->s_umount);
+		bdi_start_writeback(sb->s_bdi, get_nr_dirty_pages());
 		return 1;
-	} else
-		return 0;
+	}
+	return 0;
 }
 EXPORT_SYMBOL(writeback_inodes_sb_if_idle);
 
@@ -1172,17 +1173,18 @@ EXPORT_SYMBOL(writeback_inodes_sb_if_idl
  *
  * Invoke writeback_inodes_sb if no writeback is currently underway.
  * Returns 1 if writeback was started, 0 if not.
+ *
+ * Even if 1 is returned, writeback may not be started if memory allocation
+ * fails. This function makes no guarantees about anything.
  */
 int writeback_inodes_sb_nr_if_idle(struct super_block *sb,
 				   unsigned long nr)
 {
 	if (!writeback_in_progress(sb->s_bdi)) {
-		down_read(&sb->s_umount);
-		writeback_inodes_sb_nr(sb, nr);
-		up_read(&sb->s_umount);
+		bdi_start_writeback(sb->s_bdi, nr);
 		return 1;
-	} else
-		return 0;
+	}
+	return 0;
 }
 EXPORT_SYMBOL(writeback_inodes_sb_nr_if_idle);