On Wednesday 05 March 2003 04:40 pm, Kirk Strauser wrote:
> I killed my FreeBSD 4.8-PRE (2003-02-18) server today by exhausting the
> available mbufs.  I'd seen warnings like "All mbuf clusters exhausted,
> please see tuning(7)." in /var/log/messages, so I added
> `kern.ipc.nmbclusters="16384"' to /boot/loader.conf.local a while back.
> This server has 768MB of memory, and I run at least two copies of
> PostgreSQL (it has multiple jails) at any given time and use it to server
> NFS to a couple of Linux clients.  Today I wanted to test Bochs on one of
> the Linux machines, ran the bochsconf program, watched it run "createdisk"
> to make a 512MB disk image in my home directory, and saw the server panic
> within a few seconds.  When it came back up, I bumped nmbclusters to 32768,
> rebooted, and tried createdisk it.  This time I watched `netstat -m' as the
> dreaded "All mbuf clusters exhausted..." message began to scroll up the
> screen.  This time, the server stayed alive, but it clearly maxed out all
> available buffers.  After createdisk was finished, the mbuf usage went back
> to normal:
>     $ netstat -m
>     389/36736/131072 mbufs in use (current/peak/max):
>             389 mbufs allocated to data
>     388/32768/32768 mbuf clusters in use (current/peak/max)
>     74720 Kbytes allocated to network (33% of mb_map in use)
>     345 requests for memory denied
>     1 requests for memory delayed
>     0 calls to protocol drain routines
> My questions are these:
> 1) Is there a guideline for how many nmbclusters to allocate?  Short of
>    running out of physical memory, is there such a thing as too many?
> 2) I've already allocated 64MB to network buffering.  This seems like a
> huge amount to me.  Is it?
> 3) Should running out of mbufs be expected to crash the server, or should I
>    try to reproduce it and file a PR?

Reproducible errors are the most helpful thing a developer can have to improve 
FreeBSD's stability.  So try to reproduce it, but make sure you're doing it 
on the most recent -stable code, as your problem may already be fixed.  If 
you can update to -stable and still get that error then file a pr and ask on 
the -stable mailing list as that is the appropriate place.
        No idea on the rest, sorry,


> 4) What could createdisk have been doing to spike usage that heavily?
> 5) Could Linux's NFS client implementation have aggravated the situation?

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