4.9 network not freeing memory

[Stephen Clark]

Hi,

I realize this is a very old release but we have over a 1000 systems 
deployed so it is hard to upgrade.

Anyway we are using gre/vpn/gif. If I stress test the system with 
netperf or nttcp I eventually
run into the situation where netperf is in sbwait state and it stays 
there forever. I can't log into the machine with ssh but I can go in 
thru the console. If I try to ping localhost I get
ping: sendto: No buffer space available. The only recourse to get things 
going again is reboot.
If I do and netstat -m it shows I have mbufs available.

The system is a Duron 1.6ghz with 256 mb of memory.

What I am looking for is some direction on how to further diagnose the 
problem.

this is before the problem
$ netstat -m
2/736/131072 mbufs in use (current/peak/max):
        2 mbufs allocated to data
0/672/32768 mbuf clusters in use (current/peak/max)
1528 Kbytes allocated to network (1% of mb_map in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines

this is after the problem:

965/1376/131072 mbufs in use (current/peak/max):
        965 mbufs allocated to data
872/876/32768 mbuf clusters in use (current/peak/max)
2096 Kbytes allocated to network (2% of mb_map in use)
0 requests for memory denied
0 requests for memory delayed
0 calls to protocol drain routines

Any ideas would be greatly appreciated.
Steve