QA:Testcase Memory Pressure Based Killing

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 -r --unit systoomd_mempressure_test /usr/bin/stress-ng --brk 1 --stack 1 --bigheap 1 -t 90s

• 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
systemctl --user reset-failed systoomd_mempressure_test.service

Expected Results

• The system becomes unresponsive during the test but should respond again once stress-ng is killed.
• systemd-oomd will have killed systoomd_mempressure_test.service after about 10 seconds. stress-ng will timeout after 90 seconds, so if the the command runs to timeout, it means systemd-oomd did not kill it. You can verify by checking for log lines that say something about "Memory pressure for <...> and there was reclaim activity" and "systemd-oomd killed <...> process(es)" with journalctl.