External email: Please exercise caution

Hello,

We've noticed a recent change in how MaxRSS is reported on our cluster. Specifically, the MaxRSS value for many jobs now often matches the allocated memory, which was not the case previously. It appears this change is due to how Slurm accounts for memory when copying large files, likely as a result of moving from cgroup v1 to cgroup v2.

Here’s a simple example:

copy_file.sh
#!/bin/bash
cp /distributed/filesystem/file5G /tmp
cp /tmp/file5G ~

Two jobs with different memory allocations:

Job 1
sbatch -c 1 --mem=1G copy_file.sh
seff <jobid>
Memory Utilized: 1021.87 MB
Memory Efficiency: 99.79% of 1.00 GB

Job 2
sbatch -c 1 --mem=10G copy_file.sh
seff <jobid>
Memory Utilized: 4.02 GB
Memory Efficiency: 40.21% of 10.00 GB

With cgroup v1, this script typically showed minimal memory usage. Now, under cgroup v2, memory usage appears inflated and depends on the allocated memory, which seems wrong.

I believe this behavior aligns with similar issues raised by the Kubernetes community [1], and is consistent with how memory.current behaves in cgroup v2 [3].

According to Slurm’s documentation about cgroup v2, "this plugin provides cgroup's memory.current value from the memory interface, which is not equal to the RSS value provided by procfs. Nevertheless it is the same value that the kernel uses in its OOM killer logic." [2]

While technically correct, this seems to mark a significant change in what MaxRSS and "Memory Efficiency" actually measure and renders those metrics almost useless.

Our Configuration:
ProctrackType=proctrack/cgroup
TaskPlugin=task/cgroup,task/affinity

Question:
Is there a way to restore more realistic MaxRSS values — specifically, ones that exclude file-backed page cache — while still using cgroup v2?

Thanks,
Guillaume

References:

[1] https://github.com/kubernetes/kubernetes/issues/118916
[2] https://slurm.schedmd.com/cgroup_v2.html#limitations
[3] https://facebookmicrosites.github.io/cgroup2/docs/memory-controller.html

--
slurm-users mailing list -- slurm-users@lists.schedmd.com
To unsubscribe send an email to slurm-users-leave@lists.schedmd.com