ZFS and deadlock with {nullfs,NFS}

Joe Marcus Clarke marcus at FreeBSD.org
Wed Jun 20 17:03:12 UTC 2007

Hash: SHA1

Kris Kennaway wrote:
> On Wed, Jun 20, 2007 at 12:17:54PM -0400, Joe Marcus Clarke wrote:
>> On Wed, 2007-06-20 at 12:03 -0400, Kris Kennaway wrote:
>>> On Wed, Jun 20, 2007 at 11:53:43AM -0400, Joe Marcus Clarke wrote:
>>>> I've resurrected by amd64 Tinderbox with a ZFS base, and I've been
>>>> seeing a 100% reproducible deadlock when I use it with either localhost
>>>> NFS or nullfs.  When this occurs, the CPU is 100% idle, but I can no
>>>> longer connect via SSH, and the box will only reboot from the debugger.
>>>> I know there are some tuning bits I can tweak, but all I've run across
>>>> is for memory consumption.  Any pointers would be helpful.  I'm also at
>>>> the debugger, so if there is anything I can do to help troubleshoot why
>>>> this is happening, please let me know.  
>>>> This box is -CURRENT as of June 19, 2007.  It has a GENERIC kernel minus
>>>> devices I do not have (i.e. SMP kernel).  I am currently using nullfs
>>>> for the Tinderbox.  The process that most regularly locks up is mtree.
>>>> Here is the trace:
>>>> A full process list from the debugger can be found at
>>>> http://www.marcuscom.com/downloads/cobbler_proc.txt .
>>> 404 at the moment, but look for processes involving zil* in the
>>> backtrace.  I had to disable zil (vfs.zfs.zil_disable=1 tunable) to
>>> prevent low-memory deadlocks on my machines.  Since then it's been
>>> fine.
>> Fixed, sorry.
>>> You may also wish to use my patches (see the archives) to improve
>>> performance and low-memory behaviour.
>> Thanks for the advice.  I'll check.  I didn't think low memory since it
>> didn't look like I was using much.  Even now with the box locked, I have
>> 1035 MB free with no swap in use (this box has 2 GB total).
> By default there is only a 320 MB kmem_map into which all of zfs
> (including its buffer cache and I/O buffers) has to cram itself, so
> that is where the low memory condition may be happening.  This is one
> of the things that should be tuned to give non-terrible performance by
> actually allowing some caching to occur.

Dammit!  I always forget about KVM.  Thanks. :-}


- --
Joe Marcus Clarke
FreeBSD GNOME Team	::	gnome at FreeBSD.org
FreeNode / #freebsd-gnome
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