From owner-freebsd-net@FreeBSD.ORG  Wed May 12 17:45:06 2010
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Date: Wed, 12 May 2010 21:45:04 +0400
From: Sergey Matveychuk <sem@FreeBSD.org>
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Cc: 
Subject: tcp_input: Listen socket: Socket allocation failed due to limits
 or memory shortage
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Hello.

I was annoyed by the subject message and decided to dig it a little. The 
message appears sporadically and caused my application accept(2) error.

I've quickly discovered it's not a listen queue overflow. I've increased 
kern.ipc.somaxconn to 1024 and listen(2) backlog argument too (netstat 
-Lan output: tcp4  0/0/1024 *.8542). But without a success. (My 
application serves only 3-5 connection simultaneously). Moreover, listen 
queue overflows counter (netstat -s) was not increased.

I've decided it's a syncache or syncookie problem. First, I've set 
net.inet.tcp.syncookies_only=1. But it does not help. Second, I've set 
it back to 0 and set net.inet.tcp.syncookies=0. The messages gone.

A message I've wrote before (syncache_expand: Segment failed SYNCOOKIE 
authentication, segment rejected (probably spoofed)) of course gone too.

May be somebody who familiar with syncookies can comment it?

-- 
Sem.