Limit Application Memory Usage with systemd

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2024-10-18 18:00:14

I saw this question on KDE forum about how to limit memory usage of a specific application in KDE, using systemd specifically. I did some research on that.

man systemd.resource-control lists plenty of options that we can set to a cgroup. E.g., to limit the memory usage of a service, we can add:

The difference between this and ulimit is that ulimit is per process, while systemd resource control is per cgroup. I.e., the MemoryHigh is accounted to the sum of both the service process, and all sub-processes it spawns, and even detached processes, i.e., daemons.

Luckily, systemd allows us to create drop-in files to partially modify a service. Also, systemd considers app-org.kde.konsole@0d82cb37fcd64fe4a8b7cf925d86842f.service to be instances of a template named app-org.kde.konsole@.service. (This is how things like getty@tty3.service work.) So we can create a drop-in file named ~/.config/systemd/user/app-org.kde.konsole@.service.d/override.conf with the content:

Note: as explained above, the limit applies to the sum of Konsole and all processes it spawns. E.g., if we run kwrite in Konsole, the memory usage of kwrite will be accounted to the limit of Konsole, and the limit we set to KWrite won't apply.