Why would my server be swapping...

[Wouter van Vliet]

G'day my fellow Fedorians,

Crappy intro, huh? Anyway, I've got a question - bit of an oddity I
noticed in the output to the "free" command. I'll post that output
before I continue:

             total       used       free     shared    buffers     cached
Mem:        515536     196040     319496          0      22448     120144
-/+ buffers/cache:      53448     462088
Swap:      1052248     151476     900772

Hope the mail brings it over nice and columny. Anyway, what it shows
is 311 megabytes of free memory and 147MB used swap space. Isn't that
a bit odd, and shouldn't the server only be swapping when all (or at
least most) of the RAM is in use?

Hoping for an answer,
Wouter