[systemd-devel] umount fails on system with huge (2TiB) buff/cache

[Michal Koutný]

Hello.

On Fri, Jan 26, 2024 at 12:13:34PM +0000, Holger Kiehl <Holger.Kiehl at dwd.de> wrote:
...
> Note it states 'no limit' and one can see after some minutes it says
> it umounted /mnt/u2:
...
> Confused here since it stated on serial console output
> 
>    [  OK  ] Unmounted /mnt/u2.

Any chance your mount unit has LazyUnmount=yes?

> The only way I can get the system to reboot properly is when sending the
> following command before doing the reboot:
> 
>    echo 1 > /proc/sys/vm/drop_caches

How long does this take BTW? (Around those 10 minutes?)

> Is it possible to tell systemd-shutdown to wait longer or are there
> some other parameters I need to tune?

systemd-shutdown uses sum of values from
/proc/meminfo:{NFS_Unstable,Writeback,Dirty} to determine whether the sync
progresses. Something in block/FS layer may got stuck if it doesn't
apparently decrease.

Regards,
Michal
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