While monitoring the memory usage on a Symantec Messaging Gateway (SMG) system, the "Memory Usage" and "Memory Free" columns do not add up to the total memory available on the SMG appliance or virtual machine.
This is expected behavior due to how current linux kernels manage memory. The SMG Status > Host page only displays the "used" and "free" values for memory utilization but does not include the "shared", "buff/cache", or "available" values:
[[email protected] ~]$ free
total used free shared buff/cache available
Mem: 3861616 2001780 554708 81352 1305128 1465916
Swap: 10534904 998400 9536504
For more information on linux memory management, please see the following articles: