Hi Jason,
thank you for your reply.
From what I can tell your problem *is* the same as ours. BTW: we were
already talking about disabling swap in our nodes as a last resort. :-)
In the meantime we made some new findings: we can trigger the error when
(with cgroups/v2) we set memory.high and memory.max to the same value
(as Slurm does it in our configuration). And this error occurs with
Rocky Linux 8.x as well as with 9.x.
It does *not* get triggered when memory.high is set to the limit and
memory.max is set to some higher value or "max".
Our plans are now to check if this is also happening in RHEL. If yes we
will open a support case.
And if time permits we will check if it can be triggered with a vanilla
kernel.
Regards,
Hermann
On 3/17/23 21:34, Jason Simms wrote:
Hello,
This isn't precisely related, but I can say that we were having strange
issues with system load spiking to the point that the nodes became
unresponsive and likewise needed a hard reboot. After several tests and
working with our vendor, on nodes that we entirely disabled swap, the
problems ceased. You may have an absolutely valid need for swap, or some
configurations may in fact rely on it for whatever reason, but for now
we've chosen to disable swap on all nodes. It's interesting, however,
because I didn't really identify the culprit, and it may be related to
cgroups somehow, but regardless, disabling swap appears to be working
for us with no immediate consequences.
Warmest regards,
Jason
On Thu, Mar 16, 2023 at 10:59 AM Hermann Schwärzler
<hermann.schwaerz...@uibk.ac.at <mailto:hermann.schwaerz...@uibk.ac.at>>
wrote:
Dear Slurm users,
after opening our new cluster (62 nodes - 250 GB RAM, 64 cores each -
Rocky Linux 8.6 - Kernel 4.18.0-372.16.1.el8_6.0.1 - Slurm 22.05) for
"friendly user" test operation about 6 weeks ago we were soon facing
serious problems with nodes that suddenly become unresponsive (so much
so that only a hard reboot via IPMI gets them back).
We were able to narrow the problem down to one similar to this one:
https://github.com/apptainer/singularity/issues/5850
<https://github.com/apptainer/singularity/issues/5850>
Although in our case it's not related to Singularity but generally to
cgroups.
We are using cgroups in our Slurm configuration to limit RAM, CPUs and
devices. In the beginning we did *not* limit swap space (we are
doing so
now to work around the problem but would like to allow at least some
swap space).
We are able to reproduce the problem *outside* Slurm as well by using
the small test program mentioned in the above Singularity GitHub-issue
(https://gist.github.com/pja237/b0e9a49be64a20ad1af905305487d41a
<https://gist.github.com/pja237/b0e9a49be64a20ad1af905305487d41a>) with
these steps (for cgroups/v1):
cd /sys/fs/cgroup/memory
mkdir test
cd test
echo $((5*1024*1024*1024)) > memory.limit_in_bytes
echo $$ > cgroup.procs
/path/to/mempoc 2 10
After about 10 to 30 minutes the problem occurs.
We tried to switch to cgroups/v2. Which does solve the problem for the
manual case outside Slurm:
cd /sys/fs/cgroup
mkdir test
cd test
echo "+memory" > cgroup.subtree_control
mkdir test2
echo $((5*1024*1024*1024)) > test2/memory.high
echo $$ > test2/cgroup.procs
/path/to/mempoc 2 10
Now it runs for days and weeks without any issues!
But when we run the same thing in Slurm (with cgroups/v2 configured to
*not limit* swapping) by using
sbatch --mem=5G --cpus-per-task=10 \
--wrap "/path/to/mempoc 2 10"
the nodes still become unusable after some time (1 to 5 hours) with the
usual symptoms.
Did anyone of you face similar issues?
Are we missing something?
Is it unreasonable to think our systems should stay stable even when
there is cgroup-based swapping?
Kind regards,
Hermann
--
*Jason L. Simms, Ph.D., M.P.H.*
Manager of Research Computing
Swarthmore College
Information Technology Services
(610) 328-8102
Schedule a meeting: https://calendly.com/jlsimms
<https://calendly.com/jlsimms>
