writeback: don't resort for a single super_block in move_expired_inodes()

If we only moved inodes from a single super_block to the temporary
list, there's no point in doing a resort for multiple super_blocks.

Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 11 insertions, 1 deletions

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index b27406d51bc7..225c7316344e 100644
--- a/fs/fs-writeback.c
+++ b/fs/fs-writeback.c
@@ -336,17 +336,27 @@ static void move_expired_inodes(struct list_head *delaying_queue,
 {
         LIST_HEAD(tmp);
         struct list_head *pos, *node;
-        struct super_block *sb;
+        struct super_block *sb = NULL;
         struct inode *inode;
+        int do_sb_sort = 0;
 
         while (!list_empty(delaying_queue)) {
                 inode = list_entry(delaying_queue->prev, struct inode, i_list);
                 if (older_than_this &&
                     inode_dirtied_after(inode, *older_than_this))
                         break;
+                if (sb && sb != inode->i_sb)
+                        do_sb_sort = 1;
+                sb = inode->i_sb;
                 list_move(&inode->i_list, &tmp);
         }
 
+        /* just one sb in list, splice to dispatch_queue and we're done */
+        if (!do_sb_sort) {
+                list_splice(&tmp, dispatch_queue);
+                return;
+        }
+
         /* Move inodes from one superblock together */
         while (!list_empty(&tmp)) {
                 inode = list_entry(tmp.prev, struct inode, i_list);