Troubleshooting Windows Server VM memory usage issue ?

Hi All,

I'm running a domain controller as VM, from my Zabbix monitoring tool, I can see the memory usage is gradually decreasing day by day.

Last week, I've restarted it because the server was frozen (not-responding), now few days after the reboot, the memory usage is decreasing few hundreds of MB per day.

Note: This server is running Global Catalog, DNS and DHCP server.

What could be the steps to troubleshoot this issue ? Any suggestion would be greatly appreciated.

Thanks,