Strange ARC/Swap/CPU on yesterday's -CURRENT

[Jeff Roberson]

On Sun, 11 Mar 2018, Mark Millard wrote:

> As I understand, O. Hartmann's report ( ohartmann at walstatt.org ) in:
>
> https://lists.freebsd.org/pipermail/freebsd-current/2018-March/068806.html
>
> includes a system with a completely non-ZFS context: UFS only. Quoting that part:
>
>> This is from a APU, no ZFS, UFS on a small mSATA device, the APU (PCenigine) works as a
>> firewall, router, PBX):
>>
>> last pid:  9665;  load averages:  0.13,  0.13,  0.11
>> up 3+06:53:55  00:26:26 19 processes:  1 running, 18 sleeping CPU:  0.3% user,  0.0%
>> nice,  0.2% system,  0.0% interrupt, 99.5% idle Mem: 27M Active, 6200K Inact, 83M
>> Laundry, 185M Wired, 128K Buf, 675M Free Swap: 7808M Total, 2856K Used, 7805M Free
>> [...]
>>
>> The APU is running CURRENT ( FreeBSD 12.0-CURRENT #42 r330608: Wed Mar  7 16:55:59 CET
>> 2018 amd64). Usually, the APU never(!) uses swap, now it is starting to swap like hell
>> for a couple of days and I have to reboot it failty often.
>
> Unless this is unrelated, it would suggest that ZFS and its ARC need not
> be involved.
>
> Would what you are investigating relative to your "NUMA and concurrency
> related work" fit with such a non-ZFS (no-ARC) context?

I think there are probably two different bugs.  I believe the pid 
controller has caused the laundry thread to start being more aggressive 
causing more pageouts which would cause increased swap consumption.

The back-pressure mechanisms in arch should've resolved the other reports. 
It's possible that I broke those.  Although if the reports from 11.x are 
to be believed I don't know that it was me.  It is possible they have been 
broken at different times for different reasons.  So I will continue to 
look.

Thanks,
Jeff

>
> ===
> Mark Millard
> marklmi at yahoo.com
> ( dsl-only.net went
> away in early 2018-Mar)
>