Systemtap to predict memory upgrade needs

[Andrew Klaassen <clawsoon at yahoo dot com>]

Hi.

I'm brand new to systemtap.  I'm trying to write a script that'll monitor a currently running fileserver and tell me how often the physical disk will get hit if I double/quadruple/etc my RAM.

Here's what I've figured out so far: I need to hook into all possible read/write operations (aio_read/write, regular read/write, readv/writev, sendfile, etc).  My script then needs to duplicate the kernel buffer/paging logic, substituting my desired memory size for my actual memory size.

This seems really complicated.  (I am a lowly sysadmin, so I'm way over my head here.)  Is there a simpler way?  Is this something someone has already built?

Thanks.

Andrew