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.
# df -h
文件系统 容量 已用 可用 已用% 挂载点
/dev/mapper/centos-root 50G 9.1G 41G 19% /
devtmpfs 63G 0 63G 0% /dev
tmpfs 63G 0 63G 0% /dev/shm
tmpfs 63G 9.8M 63G 1% /run
tmpfs 63G 0 63G 0% /sys/fs/cgroup
/dev/sda2 1014M 239M 776M 24% /boot
/dev/mapper/centos-home 0.3T 147G 0.1T 2% /home
tmpfs 13G 0 13G 0% /run/user/0
stop services: apache, tomcat, mysql etc. on home
systemctl stop mysql
systemctl stop tomcat
systemctl status mysql
systemctl status tomcat
• backup the contents of /home
> tar -czvf /home/home.tgz -C /home .
• test the backup
> tar -tvf /home/home.tgz
copy /home/home.tgz to other PC • unmount home
> umount /dev/mapper/centos-home
如果显示/home正忙，且不在/home目录下，说明/home下有进程正在使用，用
fuser -m -v -i -k /home
杀死/home下的进程，再解除挂载点。但是fuser在centos7里面不是默认安装的，需要
yum install psmisc
来安装这个包。
• remove the home logical volume
> lvremove /dev/mapper/centos-home
- 扩展
/root所在的lv，增加200G ：lvextend -L +200G /dev/mapper/centos-root - 扩展/root文件系统 ：
xfs_growfs /dev/mapper/centos-root
vgdisplay
重新创建home lv 分区的大小，根据 vgdisplay 中的free PE 的大小确定
lvcreate -L 300G -n home centos
- 创建文件系统：
mkfs.xfs /dev/centos/home - 挂载
home：mount /dev/centos/home /home
• 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.
REF：