Re: nullfs and ZFS issues

Quoting Mateusz Guzik <mjguzik@gmail.com> (from Thu, 21 Apr 2022  
14:50:42 +0200):

> On 4/21/22, Alexander Leidinger <Alexander@leidinger.net> wrote:
>> I tried nocache on a system with a lot of jails which use nullfs,
>> which showed very slow behavior in the daily periodic runs (12h runs
>> in the night after boot, 24h or more in subsequent nights). Now the
>> first nightly run after boot was finished after 4h.
>>
>> What is the benefit of not disabling the cache in nullfs? I would
>> expect zfs (or ufs) to cache the (meta)data anyway.
>>
>
> does the poor performance show up with
> https://people.freebsd.org/~mjg/vnlru_free_pick.diff ?

I would like to have all the 22 jails run the periodic scripts a  
second night in a row before trying this.

> if the long runs are still there, can you get some profiling from it?
> sysctl -a before and after would be a start.
>
> My guess is that you are the vnode limit and bumping into the 1 second sleep.

That would explain the behavior I see since I added the last jail  
which seems to have crossed a threshold which triggers the slow  
behavior.

Current status (with the 112 nullfs mounts with nocache):
kern.maxvnodes:               10485760
kern.numvnodes:                3791064
kern.freevnodes:               3613694
kern.cache.stats.heldvnodes:    151707
kern.vnodes_created:         260288639

The maxvnodes value is already increased by 10 times compared to the  
default value on this system.

Bye,
Alexander.

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