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 <[email protected]>
Reviewed-by: Tejun Heo <[email protected]>
Reviewed-by: Jan Kara <[email protected]>
Signed-off-by: Jens Axboe <[email protected]>

0 files changed, 0 insertions, 0 deletions