fs: remove default_backing_dev_info

Now that default_backing_dev_info is not used for writeback purposes we can
git rid of it easily:

 - instead of using it's name for tracing unregistered bdi we just use
   "unknown"
 - btrfs and ceph can just assign the default read ahead window themselves
   like several other filesystems already do.
 - we can assign noop_backing_dev_info as the default one in alloc_super.
   All filesystems already either assigned their own or
   noop_backing_dev_info.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Tejun Heo <tj@kernel.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Signed-off-by: Jens Axboe <axboe@fb.com>

1 files changed, 1 insertions, 1 deletions

diff --git a/fs/ceph/super.c b/fs/ceph/super.c
index e350cc1611e4..5ae62587a71d 100644
--- a/fs/ceph/super.c
+++ b/fs/ceph/super.c
@@ -899,7 +899,7 @@ static int ceph_register_bdi(struct super_block *sb,
                         >> PAGE_SHIFT;
         else
                 fsc->backing_dev_info.ra_pages =
-                        default_backing_dev_info.ra_pages;
+                        VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE;
 
         err = bdi_register(&fsc->backing_dev_info, NULL, "ceph-%ld",
                            atomic_long_inc_return(&bdi_seq));