I did something similar with my VPS's (nginx/MySQL/PHP/Django via flup), but at the same time this is not as easy as just disabling the pre-forked processes. The point of those processes is that they are available. Sure, if the services on your VPS are competing for resources then yes that would be an issue. However, I would recommend that you use all the available memory, but make sure that each process stays at that memory load.
For example I have a number of FastCGI PHP processes running, each consuming up to 20MB. I tuned it so that if each one takes exactly 20MB (more or less max memory limit I set), then I still have a sliver of RAM left. That way there is no cost of starting/stopping these processes and there is maximum resource utilization.
For example I have a number of FastCGI PHP processes running, each consuming up to 20MB. I tuned it so that if each one takes exactly 20MB (more or less max memory limit I set), then I still have a sliver of RAM left. That way there is no cost of starting/stopping these processes and there is maximum resource utilization.