Fwd: Using cgroups v2 for “simple” tasks

virgo <cireyapmin@xxxxxxxxx> · Mon, 11 May 2020 06:43:51 +0000

Apologies for the duplicated message, but the one I sent earlier seems to have 
missed the target: it does not appear in the archives. Maybe I should have 
subscribed to the list before sending it…
--- Begin Message ---

Subject: Using cgroups v2 for “simple” tasks
From: virgo <cireyapmin@xxxxxxxxx>
Date: Mon, 11 May 2020 00:06:02 +0000

Greetings,

This machine is running under Fedora 32 Workstation Edition which means that, 
among other things, cgroups are under a unified hierarchy.

$ sdver=(`systemctl --version | tail -1`)
$ for i in "${sdver[@]}"; do printf "%s\n" "$i"; done | grep "hierarchy"
default-hierarchy=unified

Before the upgrade, I was using Fedora 30 and libcgroup v1, leveraging with 
that the libcgroup-tools to run some processes under certain constraints. 
Since the upgrade, my scripts broke. Here is an example:

```bash
## libcgroup v1
# Configuring a group
TGT='foo'
GRP='woe'
let M=(500 * 1024 * 1024)
let C=250000
cgcreate -a "${TGT}:${TGT}" -t "${TGT}:${TGT}" -g memory:"$GRP" -g cpu:"$GRP"
printf "%d" "$M" > /sys/fs/cgroup/memory/"$GRP"/memory.limit_in_bytes
printf "%d" "$C" > /sys/fs/cgroup/cpu/"$GRP"/cpu.cfs_quota_us

# Using the new group
cgexec --sticky -g "memory,cpu:${GRP}" <SOME-COMMAND>
```

That does not cut it anymore. I tried to follow the manual and it led me to 
write something like the file below.

# </etc/cgconfig.conf>
group woe {
    perm {
        task {
            uid = foo;
            gid = foo;
        }
    }

    memory {
        memory.high = 524288000;
    }

    cpu {
        cpu.max = 0500000 1000000;
    }
}

My limited understanding of the documentation left me with the impression 
systemd would create the cgroup `foo` after a reboot. That, of course, turned 
out to be false, I would not be here otherwise.

So, here is where your help would be greatly appreciated: how to use the 
cgcreate command and the like under libcgroup v2? Alternatively, if the way is 
by configuration files, where to create them and how to enforce what they 
stipulate?

Thanks in advance.

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