Manipulating disk cache (buf) settings

[Sven Willenberger]

We are running a PostgreSQL server (8.0.3) on a dual opteron system with
8G of RAM. If I interpret top and vfs.hibufspace correctly (which show
values of 215MB and 225771520 (which equals 215MB) respectively. My
understanding from having searched the archives is that this is the
value that is used by the system/kernel in determining how much disk
data to cache. 

If that is in fact the case, then my question would be how to best
increase the amount of memory the system can use for disk caching.
Ideally I would like to have upwards of 1G for this type of
caching/buffering. I suspect it would not be as easy as simply adjusting
vfs.hibufspace upwards but would instead involving add either a
loader.conf or kernel option of some "master" setting that affects
hibufspace, bufspace, and related tunables. Or would this involve
editing one of the system files?

Sven