I'm trying to configure my first VPS using nginx and php-fpm. I've set it up and everything is working well, but I've realized that for every user created there is a separate php-fpm pool what takes about 30 MB of memory even when idling. It wouldn't be a big problem on a huge machine, but I'm trying to do this in a 128 MB lowendbox, so it's not really nice.

I've asked in a thread on lowendbox, and received a lot of help in this thread, but I'm still confused:
http://www.lowendtalk.com/discussion/comment/123647#Comment_123647

Can you tell me some general guidelines how would it be possible to both have a secure setup and one that runs on low memory servers? Or it's not possible? What I'd like to do is very simple:
1. Have users separated, having separate accounts, scp acces, etc.
2. Only have a single php-pool for all of them, not for each one of them.

Is it possible to do it in a secure way? I mean I figured out that I can run the shared pool with a group-user, but then 'alice' can write a php script to list 'bob's files. Are there any better solution? How is it done in proper shared hosting, do they physically reserve at 64 MB RAM for each user?