It might be that the processes are genuinely eating your RAM, but on most unix-like OSs, RAM usage doesn't work quite the way people expect and it may be you're

It might be that the processes are genuinely eating your RAM, but on most unix-like OSs, RAM usage doesn't work quite the way people expect and it may be you're misunderstanding. Many pages of forked or threaded processes can be copy-on-write, so it actually costs the OS nothing to have multiple processes sharing them. They only actually become separate pages when the process actually writes to them. What this means is that you can't get a true picture of the ram usage just by adding as you will in fact be double-counting any read-only pages that are shared using COW.