mbuf leak with SMP and debug.mpsafenet=1

[Robert Watson]

On Tue, 19 Oct 2004, Andrew Gallatin wrote:

> I hooked up the em0 GbE interfaces, and that leaks nearly as bad as my
> myrinet nic (at least with a linux sender, hooked back-to-back).  Em0
> seems to be leaking at a few thoundsand pkts/sec, so I wasn't brave
> enough to do a long run.. 

Oh, I just had a thought.  Could you try this patch (perhaps with tweaks
to apply to recent kernels):

    http://www.watson.org/~robert/freebsd/netperf/20040910-atomic-mballoc.diff

I ran with this change in the netperf branch for quite a long time, but
never managed to trigger sufficient races on the allocator to result in
the counters getting off by more than a couple.  However, the reason I
updated the patch and put it on the netperf page was that Bill Paul
reported seeing fairly hefty stats errors on an SMP box at gig-e rates,
and when he tried the patch it went away.  It would be useful if you could
try the patch to make sure that we're looking at a real mbuf leak and not
an mbuf stat leak.

Robert N M Watson             FreeBSD Core Team, TrustedBSD Projects
robert at fledge.watson.org      Principal Research Scientist, McAfee Research