My AU $0.05 on this issue:

I have seen the same problems with an "overly greedy" filecache
on out-of-the-box installs of AIX, Solaris (before 5.8), Tru64,
linux and Darwin. I know where the knobs are on AIX, Solaris and
Tru64, and I can usually get the performance users demand. However,
NetBSD is the first I've seen to have the degree of flexibility it
has when tuning memory page-type priorities. Do I think the
defaults are unreasonable? Considering AIX maxperm/maxclient
defaults to 80%, Tru64 ubc-borrowpercent defaults to 20%, and our
filemax defaults to 50%, no, I think what we've got is pretty
reasonable.

Kudos for the folks responsible for those knobs - I find the
degree of flexibility they allow refreshing.

Cheers,
--
stix