ZFS hanging

[Fabian Keil]

Dennis Glatting <freebsd at pki2.com> wrote:

> On Fri, 2012-07-13 at 17:06 +0200, Fabian Keil wrote:
> > Lytochkin Boris <lytboris at gmail.com> wrote:
> > 
> > > On Thu, Jul 12, 2012 at 5:15 PM, Fabian Keil
> > > <freebsd-listen at fabiankeil.de> wrote:
> > > > fk at r500 ~ $zpool status
> > > > load: 0.15  cmd: zpool 2698 [spa_namespace_lock] 543.23r 0.00u 0.12s 0% 2908k
> > > 
> > > This sounds familiar with http://www.freebsd.org/cgi/query-pr.cgi?pr=163770
> > > Try playing with kern.maxvnodes.
> > 
> > Thanks for the suggestion, but the system is my laptop and I already
> > set kern.maxvnodes=400000 which I suspect is more than I'll ever need.
> > 
> > Currently I uses less than a tenth of this, but I'll keep an eye on
> > it the next time the issue occurs.
> > 
> > I usually reach this deadlock after losing the vdev in a single-vdev pool.
> > My suspicion is that the deadlock is caused by some kind of "failure to
> > communicate" between ZFS and the various geom layers involved.
> > 
> > I already know that losing vdevs with the pool configuration I use
> > can cause http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/162010
> > and http://www.freebsd.org/cgi/query-pr.cgi?pr=kern/162036 and I
> > suspect that the deadlock is just another symptom of the same issue.

Just to be clear: I meant the spa_namespace_lock deadlock on my system,
not the one that started this thread.

> What is the math and constraints behind kern.maxvnodes and how would a
> reasonable value be chosen?

The kernel already chooses a reasonable value for you and usually
there's no reason to overwrite it. You can find the kernel's math
at http://fxr.watson.org/fxr/source/kern/vfs_subr.c#L284 (ff).

> On some of my systems (default):
> 
> 
> iirc# sysctl -a | grep kern.maxvnodes
> kern.maxvnodes: 1097048

You can compare this with vfs.numvnodes and vfs.freevnodes if you like
(which of course depend on the load), but so far I don't remember seeing
any indication that your problem has anything to do with maxvnodes
(or block sizes for that matter).

Fabian
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 196 bytes
Desc: not available
Url : http://lists.freebsd.org/pipermail/freebsd-fs/attachments/20120713/1edc79ff/signature.pgp