mbufs problem

[z13 <z13_(_at_)_ktv_(_dot_)_lt>]

Hi all

I have little problem on my router with mbuf's.

I am running 3.3 snapshot
OpenBSD head.ktv.lt 3.3 GENERIC#42 i386

I'm using 3C990SVR95 and 3C990SVR97 ethernet cards.

Here is output of netstat -m

10541 mbufs in use:
10534 mbufs allocated to data
        1 mbuf allocated to packet headers
	6 mbufs allocated to socket names and addresses
10531/5473/8192 mbuf cluster pages in use
(current/peak/max)
24636 Kbytes allocated to network (-74% in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines

This is after I increased NMBCLUSTERS up to 16384.
After normal boot this machine works about one or two days,
after that (when no free mbuf's is available) it begin to respond to
network very slowly.
(with less value of NMBCLUSTERS mbuf's will fill up little bit faster)

It doesn't help when I tried tune sessions timeouts with pf.

It was tested with 3.1, 3.2 and now with 3.3 snapshot.
I think that kernel doesn't free unused mbufs (but why ?).

This router serves about 2500 clients.
At peak hours sessions number jumps up to ~40000.

Please tell me `where` i can tune `what` to eliminate this problem ?