Swap space problem

Hy!
Recently i had a problem with one of mine Tru64 machines.
It started to kill processes because of low amount of swap space. It said that it went below 10 %.
But when i ran swapon -s it said:
In-use space: 12 %

So, the system couldn't accept any new ssh connections plus it killed most of active ssh connections.
First thing taht i did, i restarted inetd and sshd and it solved the problem.
But i still don't know why and how it happened.
I had no swap problems so far with this machine.

The meachine has 2 GB of RAM and 4 GB of swap space which is never utilized more than 14 %.

Any ideas?

May you have many processes running as root, and these processes request more cpu and more memory and more and more ...