mbuf leakage with nfs/zfs?

[Jeremy Chadwick]

On Sat, Feb 27, 2010 at 10:53:00PM +0100, Willem Jan Withagen wrote:
> On 27-2-2010 21:32, Eirik Øverby wrote:
> >I've had a discussion with some folks on this for a while. I can easily
> >reproduce this situation by mounting a FreeBSD ZFS filesystem via
> >NFS-UDP from an OpenBSD machine. Telling the OpenBSD machine to use TCP
> >instead of UDP makes the problem go away.
> >
> >Other FreeBSD systems mounting the same share, either using UDP or TCP,
> >does not cause the problem to show up.
> >
> >A patch was suggested by Rick Macklem, but that did not solve the issue:
> >http://lists.freebsd.org/pipermail/freebsd-current/2009-December/014181.html
> 
> I concur.
> Everything in my network is now on TCP, and there is no mbuf leakage.
> I just don't get over the 5500 mark, no matter what I throw at it.
> 
> I do feel that TCP is not as well performing on a local net with Linux,
> hence the choice for UDP. But TCP is workable as next best.

I'm pulling in Robert Watson, who has some familiarity with the UDP
stack/code in FreeBSD.  I'm not sure he'll be a sufficient source of
knowledge for this specific issue since it appears (?) to be specific to
NFS; Rick Macklem would be a better choice, but as reported, he's MIA.

Robert, are you aware of any changes or implementation issues which
might cause excessive (read: leaking) mbuf use under UDP-based NFS?  Do
you know of a way folks could determine the source of the leak, either
via DDB or while the system is live?

-- 
| Jeremy Chadwick                                   jdc at parodius.com |
| Parodius Networking                       http://www.parodius.com/ |
| UNIX Systems Administrator                  Mountain View, CA, USA |
| Making life hard for others since 1977.              PGP: 4BD6C0CB |