[DRBD-user] umount /drbdpart takes >50 seconds

[Igor Cicimov]

On Fri, Dec 14, 2018 at 2:57 AM Lars Ellenberg <lars.ellenberg at linbit.com>
wrote:

> On Wed, Dec 12, 2018 at 10:16:09AM +0100, Harald Dunkel wrote:
> > Hi folks,
> >
> > using drbd umounting /data1 takes >50 seconds, even though the file
> > system (ext4, noatime, default) wasn't accessed for more than 2h.
> > umount ran with 100% CPU load.
> >
> > # sync
> > # time umount /data1
> >
> > real    0m52.772s
> > user    0m0.000s
> > sys     0m52.740s
> >
> >
> > This appears to be a pretty long time. I am concerned that there
> > is some data sleeping in a buffer that gets flushed only at umount
> > time.
> >
> > Kernel is version 4.18.0-0.bpo.1-amd64 on Debian Stretch. drbdutils
> > is 8.9.10-2. drbd.conf is attached. The bond2 interface used for
> > drbd synchronization is based upon 2 * 10 Gbit/sec NICs.
> >
> > Every insightful comment is highly appreciated.
>
> Unlikely to have anything to do with DRBD.
>
> since you apparently can reproduce, monitor
> grep -e Dirty -e Writeback /proc/meminfo
> and slabtop before/during/after umount.
>
> Also check sysctl settings
> sysctl vm | grep dirty
>

Good point, people running servers with huge amount of ram should
understand there is also a huge amount of cache that needs to get flushed
to the device before it gets removed.
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