なんとなくErrata眺めてたら

[20070116, update 20070212] Systems with very heavy network activity have been observed to have some problems with the kernel memory allocator. Symptoms are processes that get stuck in zonelimit state, or system livelocks. One partial workaround for this problem is to add the following line to /boot/loader.conf and reboot:

kern.ipc.nmbclusters="0"

Other workarounds have been discussed on the freebsd-current@ and freebsd-stable@ mailing lists.

A bugfix has been committed to HEAD and has been merged to RELENG_6.

とかなんとか。
どーなんでしょうかね。