As others have pointed out, XFS filesystem cannot be shrunk.

So your best bet is to backup /home, remove and recreate its volume in a smaller size and give the rest to your /root volume just as Koen van der Rijt outlined in his post.

• backup the contents of /home

> tar -czvf /root/home.tgz -C /home .

• test the backup

> tar -tvf /root/home.tgz

• unmount home

> umount /dev/mapper/centos-home  # 有可能有target is busy错误，使用umount -l /dev/mapper/centos-home， l表示lazy

• remove the home logical volume

> lvremove /dev/mapper/centos-home  # 有可能有Logical volume centos/home contains a filesystem in use. 使用lvremove -f /dev/mapper/centos-home，如果还不可以，使用lvremove -f /dev/mapper/centos-home 然后再lvremove -f /dev/mapper/centos-home

• recreate a new 400GB logical volume for /home, format and mount it

> lvcreate -L 400GB -n home centos

> mkfs.xfs /dev/centos/home

> mount /dev/mapper/centos-home

• extend your /root volume with ALL of the remaining space and resize (-r) the file system while doing so

> lvextend -r -l +100%FREE /dev/mapper/centos-root  # 测试，用-t

• restore your backup

> tar -xzvf /root/home.tgz -C /home

• check /etc/fstab for any mapping of /home volume. IF it is using UUID you should update the UUID portion. (Since we created a new volume, UUID has changed)

That's it.

Hope this helps.