Here we're not releasing any space, but transferring bytes from
->bytes_may_use to ->bytes_reserved. The last change to the code in
commit 
18513091af9483ba8 ("btrfs: update btrfs_space_info's
bytes_may_use timely") removed a conditional tracepoint and the logic
changed too but the tracepiont remained.
Signed-off-by: Liu Bo <bo.liu@linux.alibaba.com>
Reviewed-by: Nikolay Borisov <nborisov@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ update changelog ]
Signed-off-by: David Sterba <dsterba@suse.com>
        } else {
                cache->reserved += num_bytes;
                space_info->bytes_reserved += num_bytes;
-
-               trace_btrfs_space_reservation(cache->fs_info,
-                               "space_info", space_info->flags,
-                               ram_bytes, 0);
                space_info->bytes_may_use -= ram_bytes;
                if (delalloc)
                        cache->delalloc_bytes += num_bytes;