How can I get the current memory usage (preferably in bytes so they can be added up accurately) for all running processes individually? Can I roll up the summaries for child processes into the process that spawned them? (e.g all apache threads together).

Sometimes, my server runs out of memory and becomes unresponsive. I want to discover what is using up all the memory. Unfortunately, it's likely to not be a single process. Some programs spawn hundreds of processes, each using very little memory, but it adds up.

On a side note, is it normal for apache to spawn 200+ processes?