Using CGroups with Posit products

Control Groups are a feature of the Linux kernel that allows resource utilisation limits to be set on processes.

The two primary resources we see questions about in Support are CPU and Memory utilisation - here I will walk through how to create a Control Group limit on memory for a Workbench session.

The resources available to limit are all listed in the kernel documentation, we are looking for the section on memory.

  memory.high

  A read-write single value file which exists on non-root cgroups. The
  default is “max”.

  Memory usage throttle limit. This is the main mechanism to control memory
  usage of a cgroup. If a cgroup’s usage goes over the high boundary, the 
  processes of the cgroup are throttled and put under heavy reclaim pressure.

  Going over the high limit never invokes the OOM killer and under extreme
  conditions the limit may be breached.

  memory.max
  
  A read-write single value file which exists on non-root cgroups. The 
  default is “max”.
  
  Memory usage hard limit. This is the final protection mechanism. If a
  cgroup’s memory usage reaches this limit and can’t be reduced, the OOM
  killer is invoked in the cgroup. Under certain circumstances, the usage
  may go over the limit temporarily. In default configuration regular
  0-order allocations always succeed unless OOM killer chooses current task 
  as a victim.
  
  Some kinds of allocations don’t invoke the OOM killer. Caller could retry
  them differently, return into userspace as -ENOMEM or silently ignore in
  cases like disk readahead.
  
  This is the ultimate protection mechanism. As long as the high limit is
  used and monitored properly, this limit’s utility is limited to providing
  the final safety net.

To configure this for Workbench, we want to adjust the rstudio-launcher.service, as that is the service that creates and controls each session. Here we will set the memory.high to 2GB:

systemctl set-property rstudio-launcher.service MemoryHigh=2G

We can see that this has created a systemd control file:

[root@rocky]# cat /etc/systemd/system.control/rstudio-launcher.service.d/50-MemoryHigh.conf
# This is a drop-in unit file extension, created via "systemctl set-property"
# or an equivalent operation. Do not edit.
[Service]
MemoryHigh=2147483648

In this way, you can enforce CPU and memory limits at an OS level, rather than just for R sessions within Workbench.