In ll_statfs_internal() the call to obd_statfs->lmv_statfs() sends the MDS_STATFS RPC(s) serially for each MDT in the filesystem, unlike the obd_statfs_rqset->lov_statfs_async() call that sends the OST_STATFS RPCs in parallel to all OSTs.
It would be good to clean this code up so the MDT RPCs are also sent in a single request set, in case there are a lot of MDTs in the filesystem.
I also notice in lmv_statfs() that it isn't adding in os_bfree from the secondary MDTs into osfs. While this isn't critical for correctness today (the os_b* fields are discarded by ll_statfs_internal() for returning to userspace) this will be necessary for Data-on-MDT and is just more correct.
Also, lmv_statfs() doesn't handle the case where the individual mdc_statfs() calls return a different os_bsize, unlike lov_update_statfs() does.