No buffer space available

[Tom Ivar Helbekkmo <tih%hamartun.priv.no@localhost>]

I've been having the same problem with my amd64 system (a Dell 2850)
running current for a long time: it's been there at least since August
of 2013 (probably longer), and after upgrading to a fresh current from
about two days ago, it's still present.

When the machine gets loaded down with work, I get network pauses of
varying length, from a few seconds to a couple of minutes, where all
network activity just stops, and I get console messages from various
subsystems complaining about no buffer space available - e.g.

Sep  1 09:32:49 barsoom openvpn[2896]: write UDPv4: No buffer space available 
(code=55)

Note that the condition that causes this to happen is that the machine
has a significant non-networking workload.  During this last upgrade, it
was really bad during the building of the new release before upgrading,
and when I aborted the build job, and restarted it without the "-j 4"
parameter to build.sh, that didn't change anything.  I'm guessing it has
to do with disk I/O, and that the build process is doing enough of that
without the parallellization to trigger the problem.

Any hints as to how to either resolve this, or debug it further?

-tih
-- 
It doesn't matter how beautiful your theory is, it doesn't matter how smart
you are. If it doesn't agree with experiment, it's wrong.  -Richard Feynman