Re: nullfs and ZFS issues

On 4/21/22, Alexander Leidinger <Alexander@leidinger.net> wrote:
> Quoting Doug Ambrisko <ambrisko@ambrisko.com> (from Wed, 20 Apr 2022
> 09:20:33 -0700):
>
>> On Wed, Apr 20, 2022 at 11:39:44AM +0200, Alexander Leidinger wrote:
>> | Quoting Doug Ambrisko <ambrisko@ambrisko.com> (from Mon, 18 Apr 2022
>> | 16:32:38 -0700):
>> |
>> | > With nullfs, nocache and settings max vnodes to a low number I can
>> |
>> | Where is nocache documented? I don't see it in mount_nullfs(8),
>> | mount(8) or nullfs(5).
>>
>> I didn't find it but it is in:
>> 	src/sys/fs/nullfs/null_vfsops.c:  if (vfs_getopt(mp->mnt_optnew,
>> "nocache", NULL, NULL) == 0 ||
>>
>> Also some file systems disable it via MNTK_NULL_NOCACHE
>
> Does the attached diff look ok?
>
>> | I tried a nullfs mount with nocache and it doesn't show up in the
>> | output of "mount".
>>
>> Yep, I saw that as well.  I could tell by dropping into ddb and then
>> do a show mount on the FS and look at the count.  That is why I added
>> the vnode count to mount -v so I could see the usage without dropping
>> into ddb.
>
> 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 ?

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.

-- 
Mateusz Guzik <mjguzik gmail.com>