How to limit resource usage to save CPU+RAM for a certain process?

Question

I have a dev server on which sshd sometimes stops working because the machine runs out of RAM. Yes we are running low on memory and upgrading is not a feasible choice right now. What I want to do is to tell the machine: "Do what ever you want, but leave out 20MB and some CPU for sshd!".

How can that be done?

Answer 1

You can probably achieve something like that by using cgroups with the Memory resource controller.

I guess you'd put all your resource-consuming tasks in a limited (CPU & RAM) cgroup, and leave sshd "outside" so that it isn't restricted.

(Adding more swap, even in the form of a swap file, might be a good option though.)

Answer 2

Oh but cgroups are easy :) Install the libcgroup package. Create a /etc/cgconfig.conf:

mount {
    cpu     = /cgroup/cpu_and_mem;
    cpuacct = /cgroup/cpu_and_mem;
    memory  = /cgroup/cpu_and_mem;
}

group sshd {
        cpu {
                cpu.shares="500";
        }
        cpuacct {
                cpuacct.usage="0";
        }
        memory {
                memory.limit_in_bytes="1G";
        }
}

group nosshd {
        cpu {
                cpu.shares="500";
        }
        cpuacct {
                cpuacct.usage="0";
        }
        memory {
                memory.limit_in_bytes="1G";
        }
}

Start the cgconfig process which will create the hierarchy, cgroups, and set the limits. If that succeeds, you have two cgroups, both of which have 50% of the CPU assigned and 1G of memory available (don't know what your actual amount of available memory is; assuming it's 2G in this example). Now you just need to move all the tasks (ie all processes running on the system) from the root group into the nosshd cgroup:

cgroup]# cat tasks >> nosshd/tasks
cgroup]# echo > tasks

Then you just need to get the PID of the sshd process and move it info the sshd tasks file:

cgroup]# echo $PID >> sshd/tasks

Ta-da, you're done. You can now rest assured that sshd will always have 50% of the CPU and 1G of memory.

Answer 3

Use renice to get a higher priority for sshd, or check accounting. (acct) -> with this you can set resources for users, so run sshd with s

Answer 4

A more general solution to the problem of application resource usage is to run your applications in a container using Docker. You can then run containers with CPU and memory usage limits similar to cgroups.

docker run -c=10 -m=1g my-container