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>

3 files changed, 4 insertions, 8 deletions

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 1ec872e3a926..1afb18226da8 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -1719,7 +1719,7 @@ static int setup_bdi(struct btrfs_fs_info *info, struct backing_dev_info *bdi)
         if (err)
                 return err;
 
-        bdi->ra_pages   = default_backing_dev_info.ra_pages;
+        bdi->ra_pages = VM_MAX_READAHEAD * 1024 / PAGE_CACHE_SIZE;
         bdi->congested_fn       = btrfs_congested_fn;
         bdi->congested_data     = info;
         return 0;
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));
diff --git a/fs/super.c b/fs/super.c
index eae088f6aaae..3b4dadafdd60 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -185,8 +185,8 @@ static struct super_block *alloc_super(struct file_system_type *type, int flags)
         }
         init_waitqueue_head(&s->s_writers.wait);
         init_waitqueue_head(&s->s_writers.wait_unfrozen);
+        s->s_bdi = &noop_backing_dev_info;
         s->s_flags = flags;
-        s->s_bdi = &default_backing_dev_info;
         INIT_HLIST_NODE(&s->s_instances);
         INIT_HLIST_BL_HEAD(&s->s_anon);
         INIT_LIST_HEAD(&s->s_inodes);
@@ -863,10 +863,7 @@ EXPORT_SYMBOL(free_anon_bdev);
 
 int set_anon_super(struct super_block *s, void *data)
 {
-        int error = get_anon_bdev(&s->s_dev);
-        if (!error)
-                s->s_bdi = &noop_backing_dev_info;
-        return error;
+        return get_anon_bdev(&s->s_dev);
 }
 
 EXPORT_SYMBOL(set_anon_super);
@@ -1111,7 +1108,6 @@ mount_fs(struct file_system_type *type, int flags, const char *name, void *data)
         sb = root->d_sb;
         BUG_ON(!sb);
         WARN_ON(!sb->s_bdi);
-        WARN_ON(sb->s_bdi == &default_backing_dev_info);
         sb->s_flags |= MS_BORN;
 
         error = security_sb_kern_mount(sb, flags, secdata);