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Date:      Mon, 29 Mar 2021 10:50:25 +0200
From:      Stefan Esser <se@freebsd.org>
To:        Andrea Venturoli <ml@netfence.it>
Cc:        freebsd-current@freebsd.org
Subject:   Re: Strange behavior after running under high load
Message-ID:  <b44ef445-e1f9-82c4-6d85-341ccab16a15@freebsd.org>
In-Reply-To: <d72a7ff2-4b08-524e-5718-8378d2af9e7f@netfence.it>
References:  <58bea0f0-5c3d-4263-ebee-f939a7e169e9@freebsd.org> <d72a7ff2-4b08-524e-5718-8378d2af9e7f@netfence.it>

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From: Stefan Esser <se@freebsd.org>
To: Andrea Venturoli <ml@netfence.it>
Cc: freebsd-current@freebsd.org
Message-ID: <b44ef445-e1f9-82c4-6d85-341ccab16a15@freebsd.org>
Subject: Re: Strange behavior after running under high load
References: <58bea0f0-5c3d-4263-ebee-f939a7e169e9@freebsd.org>
 <d72a7ff2-4b08-524e-5718-8378d2af9e7f@netfence.it>
In-Reply-To: <d72a7ff2-4b08-524e-5718-8378d2af9e7f@netfence.it>

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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 ...
>=20
> 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 15:3=
5:37=20
CET 2021

> I've seen something similar: after a high load period, system crawled s=
o much=20
> that services were not answering in a reasonable time (e.g. mail would =
fail=20
> 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=20
working=20
> as mad.

No disk activity in my case. The system was idle without any load, but th=
e
issue persisted over many hours (up to the moment when I decided to reboo=
t
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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