Federico Mengozzi

How to use cgroups

Limit process memory usage on Linux

Prevent processes to eat up all your ram

Control groups allow to limit the resources usage of a collection of processes.

Configuration

To use control groups on Manjaro, it’s necessary to install the aur package libcgroup with yay -S libcgroup

Now let’s create a control groups that limits the memory usage to $2$ gb of physical memory and $2$ gb of virtual (swap) memory.

$ sudo cgcreate -t USERNAME:USERNAME -a USERNAME:USERNAME -g memory:/CGROUP_NAME
$ echo $((2 * 1024 * 1024 * 1024)) > /sys/fs/cgroup/memory/CGROUP_NAME/memory.limit_in_bytes
$ echo $((2 * 1024 * 1024 * 1024)) > /sys/fs/cgroup/memory/CGROUP_NAME/memory.memsw.limit_in_bytes

Running a process using the control groups is as easy as

$ cgexec -g memory:CGROUP_NAME PROCESS

Example

To demonstrate the effectiveness of using cgroups I run the following program first with and without a control group

int main() {
    int *x;
    while(true) {
        x = new int[1024 * 1024]
    }
}

Without control group

Although here the program seems to running just fine, it consumed all the memory on my machine ($8 GB$) and I wasn’t able to stop it with a CTRL^C. I had to wait for the program to crash.

With control group

In this case my machine is still responsive and it’s clear how the memory usage is capped. The control group seems to limiting the memory usage somewhere between 4 to 5 gb. The control groups is configured to allow 2 gb of physical memory and up to 10 gb of virtual memory. I guess this is the reason why the actual limit seems so strange.

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