Comment # 6 on bug 1033691 from zhen ren

lvcreate-usage.sh failed:

#lvcreate-usage.sh:162+ check lv_field @PREFIX@vg/LV4 lv_kernel_read_ahead
128.00k
lv_field: lv=@PREFIX@vg/LV4, field="lv_kernel_read_ahead", actual="512.00k",
expected="128.00k"

# lsblk
LVMTEST6266vg-LV4 253:8    0    8M  0 lvm

# cat /sys/dev/block/253\:8/bdi/read_ahead_kb 
512

Also test on centos 7.3.1611:
# cat /sys/dev/block/253\:2/bdi/read_ahead_kb 
4096