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check memory limits for cgroupv1 #27

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check memory limits for cgroupv1 #27

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simonbyrne
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Seems to fix issue with JuliaLang/julia#46796 (comment)

I admit I know very little about cgroups, or C programming, so this may well be incorrect, but it was able to correctly determine the cgroup limits on our Slurm cluster

@simonbyrne simonbyrne mentioned this pull request Oct 8, 2022
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simonbyrne commented Oct 8, 2022
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src/unix/linux-core.c
high = uv__read_uint64(filename);
} else {
p = strchr(buf, ':');
while (p != NULL && memcmp(p, ":memory:", 8)) {
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oh wait, I realise this isn't how cgroups work...

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Actually, I think it is correct? But it would be good for someone who understands these things to check.

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I take it slurm creates a cgroup subtree? On my cgroupv1 system, the limit sits at /sys/fs/cgroup/memory directly. It'd be useful to add a comment here about what you're doing, that's easier to review than to parse C code 🙂

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Yes, that appears to be how cgroupv1 works, e.g. https://unix.stackexchange.com/a/621576

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Apparently we're still missing something though, as on my cgroup1 system with Docker, I can't access even the memory subgroup listed in /proc/self/cgroup.

@maleadt
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maleadt commented Oct 8, 2022

The fallbacks were already intended to address cgroupv1. What is wrong with those?

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simonbyrne commented Oct 8, 2022 •
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It isn't giving the correct result on our Slurm cluster. If I do:

├ srun -t 01:10:00 --mem 2G --pty bash -l # start job with 2G of memory

├ cat /sys/fs/cgroup/memory/memory.limit_in_bytes # what is read by uv__get_constrained_memory_fallback
9223372036854771712

├ cat /proc/self/cgroup # cgroups of current process
11:blkio:/
10:memory:/slurm/uid_5184/job_28925944/step_0
9:freezer:/slurm/uid_5184/job_28925944/step_0
8:pids:/
7:cpuset:/slurm/uid_5184/job_28925944/step_0
6:net_prio,net_cls:/
5:perf_event:/
4:hugetlb:/
3:devices:/slurm/uid_5184/job_28925944/step_0/task_0
2:cpuacct,cpu:/
1:name=systemd:/system.slice/slurmd.service

├ cat /sys/fs/cgroup/memory/slurm/uid_5184/job_28925944/step_0/memory.limit_in_bytes # current memory controller cgroup
2147483648

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Any thoughts on this? I'd really like to get this into 1.9 (or ideally backported to 1.8).

@DilumAluthge DilumAluthge requested a review from maleadt October 11, 2022 22:11
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maleadt reviewed Oct 12, 2022
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LGTM. I'm sure upstream will have more comments though, so could you create a PR there once I have our pending changes merged?

src/unix/linux-core.c
high = uv__read_uint64(filename);
} else {
p = strchr(buf, ':');
while (p != NULL && memcmp(p, ":memory:", 8)) {
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I take it slurm creates a cgroup subtree? On my cgroupv1 system, the limit sits at /sys/fs/cgroup/memory directly. It'd be useful to add a comment here about what you're doing, that's easier to review than to parse C code 🙂

src/unix/linux-core.c
max = uv__read_uint64(filename);
snprintf(filename, sizeof(filename), "/sys/fs/cgroup/memory/%s/memory.soft_limit_in_bytes", p);
high = uv__read_uint64(filename);
}

if (max == 0)
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if (max == 0 || high == 0)

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maleadt commented Oct 12, 2022

Actually, I'll try to upstream it, since I'm working on that right now anyway.

@maleadt maleadt mentioned this pull request Oct 12, 2022
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Actually, I'll try to upstream it, since I'm working on that right now anyway.

Thanks, please let me know if I can do anything to help.

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maleadt commented Oct 26, 2022

I updated your PR to still correctly read out the limits I'm seeing (ref #27 (comment)) and pushed that to libuv#3754. Can you verify that works with your SLURM system?

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maleadt commented Nov 25, 2022

Superseded by #32

@maleadt maleadt closed this Nov 25, 2022
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