While building the Linux kernel with Rust support for ArchLinux, I ran into a problem where sphinx-build started using excessive amounts of RAM while building the HTML documentation.
This caused the system to become unresponsive before the OOM killer decided to just kill my user session.
Looking for a way to not have the OOM killer kill my session, but kill the build process before it uses up all my available RAM, I found https://unix.stackexchange.com/a/536046.
So, spawning the build with the following command will kill the build process as soon as it uses more than 20GB of RAM:
$ systemd-run --scope -p MemoryMax=20G --user makepkg Running scope as unit: run-r44087c0ea5d445fda135dc0db42b36ab.scope  426653 killed systemd-run --scope -p MemoryMax=20G --user makepkg