I have a webserver that's currently hosting two Wordpress sites and some java-based collaboration software. The server has 2G of memory and is currently using about 1.8G of the available memory. Right now what's on here is pretty much a pilot project that's getting negligible traffic so I think it's pretty clear that I'll be needing more memory.

I was wondering, if I was to release it, how I might anticipate my memory needs based on the traffic it gets. I've poked around on Google and what I've found has been a bit tenuous. Is there a good heuristic that one should use when calculating memory demands as a function of the base (no traffic) load on the server?

For reference, the output of free -m can be seen below:

             total       used       free     shared    buffers     cached
Mem:          2048       1832        215          0          0          0
-/+ buffers/cache:       1832        215
Swap:            0          0          0

To me this looks like actual memory used and isn't an illusion due to caching or anything else.

I figure the demands of my collaboration software will have to be experimentally tested so here's free -m without that software running:

             total       used       free     shared    buffers     cached                                     
Mem:          2048       1109        938          0          0          0                                     
-/+ buffers/cache:       1109        938                                                                      
Swap:            0          0          0   

My plan B to figure this out is to add a bunch of swap space to the server, give it some traffic and adjust according the the amount that swap gets used. I was just wondering if anyone had a good rule of thumb to estimate how much memory I should plan on in advance...or if what I'm thinking is nuts.

Many thanks in advance (I'm really quite new to this).