Control group (cgroups)

Control group (cgroups)

Kernel feature for resource management

Processes can have…

• limits
• reservations

Mostly used for CPU and memory

Exceeded memory limits result in out-of-memory (OOM) kills

Can be nested

Must be root to use cgroups v1

Demo: Control groups (cgroups) 020_advanced/170_kernel

XXX v1 or v2

Start container with 10% CPU limit:

docker run -d --name nginx --cpus=".1" nginx

Show processes belonging to container cgroup:

ID=$(docker container inspect nginx | jq -r '.[].Id')
cat /sys/fs/cgroup/cpu/docker/${ID}/cgroup.procs
cat /sys/fs/cgroup/system.slice/docker-${ID}.scope/cgroup.procs

Show CPU period and quota:

cat /sys/fs/cgroup/cpu/docker/${ID}/cpu.cfs_period_us
cat /sys/fs/cgroup/cpu/docker/${ID}/cpu.cfs_quota_us
cat /sys/fs/cgroup/system.slice/docker-${ID}.scope/cpu.max

XXX further reading

Control groups v2

XXX

cat /sys/fs/cgroup/cgroup.controllers

sed -i ‘s/GRUB_CMDLINE_LINUX=”“/GRUB_CMDLINE_LINUX=”systemd.unified_cgroup_hierarchy=1”/’ /etc/default/grub update-grub reboot