With most modern operating systems, the OS will use most of the memory as a cache.
As a result of this the SolusVM admin area clearly presents the following graphs:
The second and third greatly help to get an idea of how much memory is actually currently being used and whether more is necessary. Unfortunately, since the API does not provide this info, clients are unable to use this data to indicate whether they need to upgrade their memory.
The ability to see Memory (-cache) and Swap usage when calling vserver-infoall via API should be added.