Add large bulk IO support, e.g. make the ptlrpc be able to size 16MB IO, to improve the performance.
rpc_stats histogram does not support max_rpcs_in_flight greater than 31
request mbits isn't set properly for EINPROGRESS resend
Few 4 MB BRW rpcs from readahead path
Lustre Manual - Large Bulk IO
add blk_plug into osd-ldiskfs when do bio