On 6/28/05, Rolf Sommerhalder <rolf dot sommerhalder at alumni dot ethz dot ch> wrote:
> My generic-PC 1.2b8 runs as a filtering bridge on a 4 Mbit/s symmetric
> connection and after 3 days uptime shows in the syslog:
>     /kernel: All mbufs exhausted, please see tuning(7).
> 
> The bridge apparently still works, even though log outputs is severly
> limited to a few lines only (I had set it at 200 lines).
> 
> output of 'netstat -m' is:
> 
> $ netstat -m
> 9468/9536/9536 mbufs in use (current/peak/max):
>         100 mbufs allocated to data
>         9368 mbufs allocated to packet headers
> 69/198/2384 mbuf clusters in use (current/peak/max)
> 2780 Kbytes allocated to network (38% of mb_map in use)
> 46 requests for memory denied
> 0 requests for memory delayed
> 6 calls to protocol drain routines
> 
> Any hints of ehat I should try? (If needed, I can compile the kernel and
> produce a new custom image, no problem.)
> 
> Rolf
> 

You need to up the max number of network memory buffers, using:
> sysctl -w kern.ipc.nmbclusters=X

For a value for X, considering memory and usage of the machine, here
is the relevant bit from tuning(7):
     kern.ipc.nmbclusters may be adjusted to increase the number of network
     mbufs the system is willing to allocate.  Each cluster represents approx-
     imately 2K of memory, so a value of 1024 represents 2M of kernel memory
     reserved for network buffers.  You can do a simple calculation to figure
     out how many you need.  If you have a web server which maxes out at 1000
     simultaneous connections, and each connection eats a 16K receive and 16K
     send buffer, you need approximately 32MB worth of network buffers to deal
     with it.  A good rule of thumb is to multiply by 2, so 32MBx2 = 64MB/2K =
     32768.  So for this case you would want to set kern.ipc.nmbclusters to
     32768.  We recommend values between 1024 and 4096 for machines with mod-
     erates amount of memory, and between 4096 and 32768 for machines with
     greater amounts of memory.  Under no circumstances should you specify an
     arbitrarily high value for this parameter, it could lead to a boot-time
     crash.  The -m option to netstat(1) may be used to observe network clus-
     ter use.  Older versions of FreeBSD do not have this tunable and require
     that the kernel config(8) option NMBCLUSTERS be set instead.

ie: it depends what you're using it for and how much memory it has.

--g'luck
gm