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There are plenty of questions and answers about constraining the resources of a single process, e.g. RLIMIT_AS can be used to constrain the maximum memory allocated by a process that can be seen as VIRT in the likes of top. More on the topic e.g. here Is there a way to limit the amount of memory a particular process can use in Unix?

setrlimit(2) documentation says:

A child process created via fork(2) inherits its parent's resource limits. Resource limits are preserved across execve(2).

It should be understood in the following way:

If a process has a RLIMIT_AS of e.g. 2GB, then it cannot allocate more memory than 2GB. When it spawns a child, the address space limit of 2GB will be passed on to the child, but counting starts from 0. The 2 processes together can take up to 4GB of memory.

But what would be the useful way to constrain the sum total of memory allocated by a whole tree of processes?

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  • Releated: unix.stackexchange.com/questions/1424/…
    – slm
    Jun 4, 2014 at 12:37
  • 7
    I'd take a look at cgroups.
    – slm
    Jun 4, 2014 at 12:38
  • @slm Thanks! Sounds like cgroups is something to try. The only working solution this far (besides an ugly way of summing memory using PS and killing the parent process if above limit) that might work is using some form of a container (lxc or the likes).
    – jpe
    Jun 4, 2014 at 12:55
  • Yeah - the tools I'm aware of do not do a group, just single processes, but given how cgroups work for VM technologies like LXC and Docker I'd expect it to do what you want.
    – slm
    Jun 4, 2014 at 13:00
  • 1
    If it's Linux put the parent PID in its own namespace and control it and all its children that way. Here's an introductory answer to that concept: unix.stackexchange.com/a/124194/52934
    – mikeserv
    Jun 7, 2014 at 20:53

3 Answers 3

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+50

I am not sure if this answers your question, but I found this perl script that claims to do exactly what you are looking for. The script implements its own system for enforcing the limits by waking up and checking the resource usage of the process and its children. It seems to be well documented and explained, and has been updated recently.

As slm said in his comment, cgroups can also be used for this. You might have to install the utilities for managing cgroups, assuming you are on Linux you should look for libcgroups.

sudo cgcreate -t $USER:$USER -a $USER:$USER -g memory:myGroup

Make sure $USER is your user.

Your user should then have access to the cgroup memory settings in /sys/fs/cgroup/memory/myGroup.

You can then set the limit to, lets say 500 MB, by doing this:

echo 500000000 > /sys/fs/cgroup/memory/myGroup/memory.limit_in_bytes

Now lets run Vim:

cgexec -g memory:myGroup vim

The vim process and all its children should now be limited to using 500 MB of RAM. However, I think this limit only applies to RAM and not swap. Once the processes reach the limit they will start swapping. I am not sure if you can get around this, I can not find a way to limit swap usage using cgroups.

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  • The proposed solution does make it possible to limit the resident set size of a tree of processes. The behaviour seems to be different from RLIMIT_AS: it is possible to malloc more memory than is the limit, however it seems not to be possible to actually use more.
    – jpe
    Jun 13, 2014 at 17:03
  • By default, the cgroup memory limit applies only to (approximately) the physical RAM use. There's a kernel option (CONFIG_MEMCG_SWAP) to enable swap accounting; see the kernel docs for details. Jan 23, 2015 at 15:47
  • 1
    On fedora, sudo yum install libcgroup-tools
    – jozxyqk
    Mar 10, 2015 at 11:46
  • Note that if your OS is running systemd (pretty much all Linux distros these days) you're not supposed to use cgmanager nor cgcreate as far as I know. I think the officially supported systemd way is to use systemd-run --scope -p MemoryLimit=500M ... but it has been buggy in many distros so make sure to test if it actually works with your distro. In my experience, some versions will silently fail – they will run the command but will not limit the memory usage. May 9 at 9:29
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https://unix.stackexchange.com/a/536046/4319:

On any systemd-based distro you can also use cgroups indirectly through systemd-run. E.g. for your case of limiting pdftoppm to 500M of RAM, use:

systemd-run --scope -p MemoryLimit=500M pdftoppm

...

3

I created a script that does this, using commands from cgroup-tools to run the target process in a cgroup with limited memory. See this answer for details and the script.

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  • 1
    Thanks for short cgm guide, it was useful Sep 18, 2017 at 16:20
  • According to Poettering (the creator of systemd) you should not run cgmanager in a system that's running with systemd (that is, any modern Linux distro). Your disto is supposed to use cgroupv2 and you can run systemd-run --user -p MemoryMax=42M ... – however if your system is not cgroupv2 compatible, that command will appear to work but the memory usage is not actually limited in practice. Sep 4, 2021 at 15:34

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