Re: ZFS deadlock in 14

On 22.08.2023 14:24, Mark Millard wrote:
> Alexander Motin <mav_at_FreeBSD.org> wrote on
> Date: Tue, 22 Aug 2023 16:18:12 UTC :
> 
>> I am waiting for final test results from George Wilson and then will
>> request quick merge of both to zfs-2.2-release branch. Unfortunately
>> there are still not many reviewers for the PR, since the code is not
>> trivial, but at least with the test reports Brian Behlendorf and Mark
>> Maybee seem to be OK to merge the two PRs into 2.2. If somebody else
>> have tested and/or reviewed the PR, you may comment on it.
> 
> I had written to the list that when I tried to test the system
> doing poudriere builds (initially with your patches) using
> USE_TMPFS=no so that zfs had to deal with all the file I/O, I
> instead got only one builder that ended up active, the others
> never reaching "Builder started":

> Top was showing lots of "vlruwk" for the cpdup's. For example:
> 
> . . .
>   362     0 root         40    0  27076Ki   13776Ki CPU19   19   4:23   0.00% cpdup -i0 -o ref 32
>   349     0 root         53    0  27076Ki   13776Ki vlruwk  22   4:20   0.01% cpdup -i0 -o ref 31
>   328     0 root         68    0  27076Ki   13804Ki vlruwk   8   4:30   0.01% cpdup -i0 -o ref 30
>   304     0 root         37    0  27076Ki   13792Ki vlruwk   6   4:18   0.01% cpdup -i0 -o ref 29
>   282     0 root         42    0  33220Ki   13956Ki vlruwk   8   4:33   0.01% cpdup -i0 -o ref 28
>   242     0 root         56    0  27076Ki   13796Ki vlruwk   4   4:28   0.00% cpdup -i0 -o ref 27
> . . .
> 
> But those processes did show CPU?? on occasion, as well as
> *vnode less often. None of the cpdup's was stuck in
> 
> Removing your patches did not change the behavior.

Mark, to me "vlruwk" looks like a limit on number of vnodes.  I was not 
deep in that area at least recently, so somebody with more experience 
there could try to diagnose it.  At very least it does not look related 
to the ZIL issue discussed in this thread, at least with the information 
provided, so I am not surprised that the mentioned patches do not affect it.

-- 
Alexander Motin