Strange behavior after running under high load

[Stefan Esser]

Am 29.03.21 um 08:45 schrieb Andrea Venturoli:
> On 3/28/21 4:39 PM, Stefan Esser wrote:
>> After a period of high load, my now idle system needs 4 to 10 seconds to
>> run any trivial command - even after 20 minutes of no load ...
> 
> High CPU load or high disk load?

High CPU load, 3 times the number of CPU threads in this particular
batch run.

Less than 10 files of less than 100 KB per second have been written.

> ZFS? Snapshots?

ZFS and automatic snapshots of the file system every hour.

> 12.x? 13.x?

-CURRENT as of some 24 hours before the issue occurred:

FreeBSD 14.0-CURRENT #33 main-n245694-90d2f7c413f9-dirty: Sat Mar 27 15:35:37 
CET 2021

> I've seen something similar: after a high load period, system crawled so much 
> that services were not answering in a reasonable time (e.g. mail would fail 
> with "no such mailbox"!).

Program start-up was very slow, but interactive response once running was
normal (e.g. execution of internal shell commands like "echo *").

> Even rebooting didn't fix it, until I deleted some autosnapshots.

Rebooting fixed it on my case.

> top or other tools would show no disk activity, although the disks were 
working 
> as mad.

No disk activity in my case. The system was idle without any load, but the
issue persisted over many hours (up to the moment when I decided to reboot
the system to get it back into a usable state).

> Not sure it's the same case you experienced, though.

Probably not, but you seem to have hit another case were a resource limit
was reached and the system did not gracefully deal with the situation.

Thanks for replying ...

Regards, STefan

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