[root@mds-3-1 000-bench-scripts]# lctl set_param osc.bb-*.max_dirty_mb=0
osc.bb-OST0000-osc-ffff88102eeb3000.max_dirty_mb=0
error: set_param: setting /proc/fs/lustre/osc/bb-OST0000-osc-ffff88102eeb3000/max_dirty_mb=0: Numerical result out of range

In the documentation is reported the range between 0 and 2048. Probably this is related to the recent activity to autotune max_dirty_mb