ZFS performance issues (solved?!)

Jeremy Chadwick koitsu at FreeBSD.org
Mon Sep 1 10:53:00 UTC 2008

On Mon, Sep 01, 2008 at 05:48:34AM -0500, Wes Morgan wrote:
> On Mon, 1 Sep 2008, John Birrell wrote:
>> For those people experiencing a performance degradation since the 
>> DTrace import, please update your copy of  
>> src/sys/cddl/compat/opensolaris/kern/opensolaris_kmem.c by either cvsup 
>> of direct edit to remove "#define KMEM_DEBUG".
>> You only need to rebuild the opensolaris kernel module after this  
>> change. The code is shared between ZFS and DTrace via the opensolaris  
>> kernel module.
>> This is also the reason why you found it necessary to add KDB, DDB and  
>> STACK to your kernel. After removing KMEM_DEBUG, you won't need those.
>> Please confirm that this solves the problem you have been seeing.
> 8 or so hours later and everything is good here.
> One other suggestion, the "opensolaris" module that is now required for  
> zfs is not mentioned anywhere in UPDATING. Users of "MODULES_OVERRIDE"  
> will likely find themselves with a system that will not boot without  
> manual intervention, sometimes even requiring a live cd. A headsup or  
> warning would probably be appreciated by other zfs'ers.

I second this motion.  Upon rebuilding my system this morning, I was
surprised to see the kernel printf()s about OpenSolaris and CDDL, and
could find no mention of what purpose the module served.  I'm assuming
it's a module with some centralised code-pieces that DTrace and ZFS
share, but I don't have any confirmation of this.

| 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 |

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