First of all, I know how Linux uses memory for disk caching (http://www.linuxatemyram.com/), but this seems to be something different.
First of all, I run htop. The total memory usage %s of all running processes equals just above 50%, and the same result is shown when I add up the real memory usage of all of the running processes. However, htop lists my memory usage as 1381/1536MB.
Looking around, I found that I should check free -m, to see if some of my memory was being used for disk caching. Alas, free just displays this:
total used free shared buffers cached Mem: 1536 1381 154 0 0 0 -/+ buffers/cache: 1381 154 Swap: 0 0 0
I'm now very confused. Where is all this extra memory going? Did Linux "eat my RAM"?
EDIT: Sorry for causing some confusion, this VPS is running on OpenVZ.