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Description

This test case tests that systemd-oomd will kill a cgroup with the most pgscans when memory pressure on user@$UID.service exceeds 10% (or whatever was defined in systemd-oomd-defaults).

Setup

  • This test case should be performed on either bare-metal or virtual machines.
  • Check that you are running systemd 248~rc1 or higher with systemctl --version.
  • Ensure the systemd-oomd-defaults package is installed (included with Fedora 34).
  • You will also need to install stress-ng.
  • Boot the system and log in as a regular user.
  • So as not to trigger the swap policy for systemd-oomd, create an override with the following commands (don't forget to remove this file and systemctl daemon-reload to restore the settings afterwards):
sudo mkdir /etc/systemd/system/-.slice.d/
printf "[Slice]\nManagedOOMSwap=auto" | sudo tee /etc/systemd/system/-.slice.d/99-test.conf
sudo systemctl daemon-reload

How to test

  • Check that systemd-oomd is running:
systemctl status systemd-oomd
  • Check that the systemd-oomd-defaults policy was applied by running oomctl and verifying that "/user.slice/user-$UID.slice/user@$UID.service/" is listed as a path under "Memory Pressure Monitored CGroups" along with some stats. "Swap Monitored CGroups" should show no paths since we put in an override.
  • Now run the test:
systemd-run --user --scope /usr/bin/stress-ng --brk 0 --stack 0 --bigheap 0 --timeout 120s
  • Make sure to clean up the override and reset the test unit when you're done:
sudo rm /etc/systemd/system/-.slice.d/99-test.conf
sudo systemctl daemon-reload

Expected Results

  • The system becomes unresponsive during the test but should respond again once stress-ng is killed.
  • If the main stress-ng was killed, the command will print "Killed" and a non-zero exit code. If it runs to completion, it say something about "successful run" and exit 0.
  • systemd-oomd will have killed all the processes before the 120 second timeout. stress-ng may take some time to build up pressure. If the the command runs to timeout, it means systemd-oomd did not kill it.
  • You can verify by checking for some of the relevant log lines with journalctl: "Memory pressure for <...> and there was reclaim activity" or "systemd-oomd killed <...> process(es)"



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