mbuf leak with SMP and debug.mpsafenet=1

[Andrew Gallatin]

Robert Watson writes:
 > 
 > 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.

Aha!

That seems to be it (a stats leak).  This is kind of a shame, since
the last thing a P4 needs is more atomic ops :-(

I think there may have been a real leak in the past; at least I ran
a box out of mbufs a week ago.  It only came back when I ifconfig'ed
down my driver, freeing a bunch of mbufs.  But this was before green's
recent mbuf leak fix, and in the middle of driver development.  So who
knows..


Drew