This argument is unused since commit 
953651eb308f ("btrfs: factor out
helper adding a page to bio") and commit 
1b36294a6cd5 ("btrfs: call
submit_bio_hook directly for metadata pages") reworked the way metadata
bio submission is handled.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
 }
 
 blk_status_t btrfs_submit_metadata_bio(struct inode *inode, struct bio *bio,
-                                      int mirror_num, unsigned long bio_flags)
+                                      int mirror_num)
 {
        struct btrfs_fs_info *fs_info = btrfs_sb(inode->i_sb);
        blk_status_t ret;
 
                                   struct page *page, u64 start, u64 end,
                                   int mirror);
 blk_status_t btrfs_submit_metadata_bio(struct inode *inode, struct bio *bio,
-                                      int mirror_num, unsigned long bio_flags);
+                                      int mirror_num);
 #ifdef CONFIG_BTRFS_FS_RUN_SANITY_TESTS
 struct btrfs_root *btrfs_alloc_dummy_root(struct btrfs_fs_info *fs_info);
 #endif
 
                btrfs_submit_data_bio(tree->private_data, bio, mirror_num,
                                            bio_flags);
        else
-               btrfs_submit_metadata_bio(tree->private_data, bio,
-                                               mirror_num, bio_flags);
+               btrfs_submit_metadata_bio(tree->private_data, bio, mirror_num);
        /*
         * Above submission hooks will handle the error by ending the bio,
         * which will do the cleanup properly.  So here we should not return