Hi, almut!
Thank you so much for the answer!

I have updated the 24h top snapshot - I've taken it right now.
Probably now you can tell more on the subject?

Thanks, I wasn't aware that Linux may not release the memory (for example when the process dies). My assumption was misleading.

At the moment the server is running fast and stable.
Of course I'm happy, but I want to know the limits.

I'm afraid of swapping effect. I don't have an idea how to calculate the maximum number of mod_perl instances that can run stable at the same time (without swapping). So I could set MaxClients effectively.

Thanks again for the clarification on Linux memory management.

Pavel