OBSD firewall - Interrupts sky rocketting / malloc: out of space into ddb?

[Jatin Nansi <jatin_(_dot_)_nansi_(_at_)_timesgroup_(_dot_)_com>]

Hi all,

I have a OpenBSD 2.9 (ipf) firewall. This is on a P3 866 MHz and 512MB
RAM 40 G HDD. The memory and HDD have plenty of capacity free.
Since today morning, the firewall seems to have slowed down quite a lot.
Normally, the CPU usage on the system stays under 25 %. But
today it seems to be shooting above 90 %.  When I run top to see what is 
happening,
I see that the % of CPU utilization for interrupts is consistently above 
80 %.

Every few hours, the server hangs, and I get the following:

Panic: malloc: out of space in kmem_map
stopped at     - Debugger +0x4: movl %ebp, %esp


I will be grateful if anyone can suggest what I need to do, and what
the problem area is. This is a bit urgent.

I know I should probably upgrade to 3.1 and pf, but that will take a while
atleast.

TIA

Jatin