买的是2H2G，为什么内存实际只有1.6G，最少也该有1.8G吧？

root@aliyun:~# dmidecode -t memory | grep Size: | grep -v "No Module Installed"
Size: 2 GB
root@aliyun:~# free -h
total used free shared buff/cache available
Mem: 1.6Gi 707Mi 105Mi 6.0Mi 796Mi 705Mi
Swap: 2.0Gi 0B 2.0Gi