Intro
Red Hat provide a clear explanation of what control groups (cgroups) are – https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/resource_management_guide/chap-introduction_to_control_groups
TL/DR:
cgroups allow for system resources to be limited for certain user’s processes, which are defined in configuration files. This is useful e.g. if you wish to limit a compiler’s maximum memory usage and avoid it grinding the system to a halt.
Prerequisites
sudo yum list installed libcgroup-tools
If not installed, run
sudo yum install libcgroup-tools -y
Creating cgroups
lssubsys
The default syntax of /etc/cgconfig.conf, the default control group configuration file, is:
/etc/cgconfig.conf
group <groupname> {
[permissions] #optional
<controller> {
<param name> = <param value>
...
}
...
}
If this is your first time configuring control groups on a system, configure the service to start at boot:
sudo systemctl enable cgconfig
Start the service:
sudo systemctl start cgconfig
Once you have created control groups, you need to modify /etc/cgrules.conf, which assigns user processes to control groups:
NB: the <process> parameter is optional
<user>:<process> <controllers> <controlgroup>
If this is the first time control groups are created on a particular system, configure the service to start at boot:
sudo systemctl enable cgred
Start the service:
sudo systemctl start cgred
Example: Limiting PyCharm memory usage to 40% of total RAM & Swap
awk '/MemTotal/{printf "%d\n", $2 * 0.4}' < /proc/meminfo
3931969
Work out 40% of total system swap in kB:
awk '/SwapTotal/{printf "%d\n", $2 * 0.4}' < /proc/meminfo
2018507
Add the two together: 3931969 + 2018507 = 5950476
Create the control group and set memory limits:
/etc/cgconfig.conf
group pycharm {
memory {
memory.limit_in_bytes = 3931969k;
memory.memsw.limit_in_bytes = 5950476k;
}
}
Start the service:
sudo systemctl start cgconfig
This will create the pycharm cgroup under /sys/fs/cgroup/memory, owned by root as we did not specify any custom permissions:
ls -l /sys/fs/cgroup/memory | grep pycharm
drwxr-xr-x 2 root root 0 Jun 1 08:27 pycharm
Assign all users’ PyCharm processes to the control group:
NB: Find out process’ path if it is not an alias. In this example pycharm → /usr/local/bin/pycharm → /opt/pycharm-community-2017.3.4/bin/pycharm.sh
*:pycharm memory pycharm
Start the service:
sudo systemctl start cgred
Check the cgroups are correctly configured i.e. launching pycharm populates the files in /sys/fs/cgroup/memory/pycharm:
#Before running pycharm
cat /sys/fs/cgroup/memory/pycharm/memory.usage_in_bytes
0
#Launch pycharm process
pycharm &
#Check mem usage file is populated
cat /sys/fs/cgroup/memory/pycharm/memory.usage_in_bytes
934385456
Example: Stress testing memory in a cgroup
This can be done by adding the stress command to the cgroup:
<user>:stress memory <groupname>
Confirm that the stress process can reach the cgroup memory limit, e.g. 40% of total RAM:
cat /sys/fs/cgroup/memory/<groupname>/memory.usage_in_bytes
0
#Start stress process
stress --vm-bytes $(awk '/MemTotal/{printf "%d\n", $2 * (40 / 100);}' < /proc/meminfo)k --vm-keep -m 1
cat /sys/fs/cgroup/memory/pycharm/memory.usage_in_bytes
3879653376
#Use CTRL+C to stop the stress process
Confirm that the stress process is killed if it tries to use more RAM than permitted e.g. 80% of RAM:
cat /sys/fs/cgroup/memory/<groupname>/memory.usage_in_bytes
0
#Start stress process and confirm it is killed using sig 9
stress --vm-bytes $(awk '/MemTotal/{printf "%d\n", $2 * (80 / 100);}' < /proc/meminfo)k --vm-keep -m 1
stress: info: [89346] dispatching hogs: 0 cpu, 0 io, 1 vm, 0 hdd
stress: FAIL: [89346] (415) <-- worker 89347 got signal 9
stress: WARN: [89346] (417) now reaping child worker processes
stress: FAIL: [89346] (451) failed run completed in 6s
