mbuf leakage with nfs/zfs?

[Daniel Braniss]

> 
> 
> On Sat, 27 Feb 2010, Jeremy Chadwick wrote:
> 
> >> 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.
> >
> > NFS; Rick Macklem would be a better choice, but as reported, he's MIA.
> >
> 
> Not exactly MIA, but only able to read email from time to time at this
> point. I don't know when I'll be able to do more than that.
> 
> So, it does sound like it is UDP specific. Robert mentioned one scenario,
> which was an infrequently executed code path that is being tickled and it
> has a missing m_freem().
> 
> One thing someone could try is switching to the experimental nfs server
> ("-e" on both mountd and nfsd) and see if the leak goes away. If it does
> go away, it is almost certainly the above in the regular nfs server code.
> 
runing with the experimental nfs server all is ok!
(at least I can't see any mbuf leakage :-)

so now that we can  assume that the problem is in NFS/UDP writes via
classic nfsserver, where to look?

> If it doesn't go away, the problem is more likely in the krpc or the
> generic udp code. (When I looked at svc_dg.c, I could only spot one
> possible leak and you've already determined that patch doesn't help.
> The other big difference when using udp on the FreeBSD8 krpc is the
> reply cache code. I seem to recall it's an lru cache with a fixed upper
> bound, but it might be broken and leaking.
> 
> If you change the server to set sp_rcache = NULL in the initialization
> function in sys/nfsserver/nfs_srvkrpc.c, I think that disables the replay
> cache. You wouldn't want to run this way in production, but it would 
> determine if the leak is in it.
> 
> Change the 3 lines in nfsrv_init() to:
> nfsrv_pool->sp_rcache = NULL;
> nfsrv_pool->sp_assign = NULL;
> nfsrv_pool->sp_done = NULL;
> 
> and I think the krpc replay cache will be disabled.
> 
> Good luck with it and please report back if you get to try the above.
> 
> I'll get back to committing etc one of these days, rick

just keep sending insights/pointers and enjoy life

	danny