Re: ZFS tunable parameters

[Brad Spencer <brad%anduin.eldar.org@localhost>]

Greg Troxel <gdt%lexort.com@localhost> writes:

[snip]

>> I have been struggling with ZFS on a 8 to 16GB DOMU build system for
>> quite a while and with this patch and setting the values to what you
>> have listed I was able to perform my abuse builds without any problems
>> at all.  100% workable with 4 parallel builds all using the 2 CPUs I
>> give to the DOMU.  Before this I could do one or two full system
>> builds before I would have to reboot the build box and I was pretty
>> much unable to do more than 2 parallel builds at a time without
>> locking the system up.  Clamping the size of the ARC seems to be the
>> key.  One work around I was trying to use was setting the maxvnodes to
>> a very low value and that work around could be removed as well.
>
>> I am running this on a -current as of 2026-07-15.  This find is very
>> much appreciated.  Thanks again.
>
> Interesting that you are still having lockups on current.  It has a lot
> of locking fixes (also in 11, not in 10).

The previous kernel wasn't all that new, in fact, it was pretty old.  I
noted the locking fixes as they rolled by in source-change, but until
now didn't have time to try anything newer.  It is *entirely* possible
that there is more than one thing doing on here.  It is also true that I
don't know if I could make a unmodified -current hang up.  I was mostly
just pleased to see the nice improvement.

> My guess is that reducing arc is a workaround, not a fix, and is
> avoiding the locking bugs by leaving more free.  Still, not crashing is
> good....   I don't mean to say we shouldn't merge the patch, or that it
> isn't helpful to be able to set/observe -- only that there is deeper
> trouble.

In as much as I was able to tell, the hangs I saw mostly had to do with
running out of some sort of memory in a way that the system could not
recover from or could not prevent.  This was the first time in a very
long time that I was able to push the build system as hard as I wanted
to.



-- 
Brad Spencer - brad%anduin.eldar.org@localhost