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>

diff --git a/fs/fs-writeback.c b/fs/fs-writeback.c
index b27406d..225c731 100644 (file)
--- 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);