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Date:      Tue, 1 Jan 2002 14:39:30 -0500
From:      Derrick Norris <derrick@norris-net.com>
To:        freebsd-questions@freebsd.org
Subject:   MAXUSERS in 4.5-PRE and relation to NMBCLUSTERS/mbufs
Message-ID:  <200201011939.g01JdVD01904@visar.norris-net.com>

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In my kernel configs for 4.3 and 4.4, I had always set MAXUSERS=64.  
When I built world to 4.5-PRERELEASE, I set this to 0 in kernel 
config to make use of the new autosizing feature.

When reviewing my daily run output from yesterday, I noticed a couple 
of times the message buffer was flooded with messages saying:
  m_calloc failed, consider increase NMBCLUSTERS value
  m_retryhdr failed, consider increase mbuf value
  rl0: out of mbufs, tried to copy NNN bytes.

At the same time, my maillog showed:
  sendmail[82]: rejecting connections on daemon MTA: load average: NN
where load average went from 26 to 48 and back to 14 before sendmail 
said "accepting connections" again.

I had never seen these messages while running 4.3 or 4.4 with 
maxusers=64, or since building world to 4.5-PRE on Dec. 29 until 
yesterday, nor have they repeated since they showed in yesterday's 
logs.

Looked at documentation and saw that maxusers,nmbclusters, and mbufs 
are related.  The strange thing is, looking up my current values on 
4.5-PRE using sysctl shows kern.maxusers=252, 
kern.ipc.nmbclusters=4544, and kern.ipc.mbufs=18176 -- much larger 
than the values would have been when I set maxusers manually.

So why would my running at 64 maxusers before not have shown this 
problem, but messages showed when maxusers is at 252 autosized (or 
did system auto-adjust size after the messages yesterday)?  Should I 
once again force maxusers value in kernel config, and if so to what 
value?  64 like it was before, or closer to the autosized value, say 
something like 256?

Or was this all the result of some kind of hiccup in sendmail, or 
somebody trying to relay a bunch of crap through my box or otherwise 
attack it?

So many questions...

Thanks for any insight,
Derrick



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