This question is somewhat related to:
    http://mail-index.netbsd.org/tech-net/2006/03/24/0010.html

I have a NetBSD 2.1_Stable (tools/userland and kernel) i386 system
with 256M of physical ram w/256M of swap.

I'm using ipf which grabs memory from the kernel VM pool (I state that
like I know what I'm talking about, but I may be abstracting behavior
rather than understanding details...).

In order to increase available memory for large ipf rule sets,
I have been increasing the kernel pool by tuning:
options NKMEMPAGES=98352  #~196M
in my kernel config file.

This has helped up to a point. But...

Q1: How large can/should I set this as a percentage of physical ram?
Does it matter?

The problem I'm having is that I want to increase the number
of ipf filter rules, but as I add more rules I can just watch as
rule loading eats away at free memory until...

I get an error (from ipf?) that it cannot allocate memory and at that
point the system grinds to a near or complete halt. Often I have
to perform a hard reset! *****

Q2: Is there some way to prevent an in kernel process (ipf) from
taking my free memory so low that it freezes my system?

I have also noticed that if I flush the filter rules (ipf -F a),
the amount of free memory does not come back up.

Q3: Is this normal behavior? If not, is this a kernel/memory management
bug or more likely to be a problem in ipf? How can I help diagnose?

Thanks!