Spawn children in separate process group(s)

[axelkar]

I'd like to start with an appreciation of spawning children in systemd scopes. Thank you! I love that feature!

I'm currently using earlyoom with the -g flag, and all processes spawned by Niri (including Firefox) and Niri itself are in the same process group. This just led to everything being killed when Firefox was the target.

Note: GNOME hasn't fixed this: https://github.com/rfjakob/earlyoom/blob/master/MANPAGE.md#-g

Or should I just switch to systemd-oomd? Does it support user scopes?

[YaLTeR]

The main reason I didn't reset the process group is that I don't know if it's expected behavior or what the actual consequences are. Honestly spawning processes on Linux feels like every single of its million features defaults to the exactly wrong behavior, and you're somehow expected to know about all of them to fix them one by one.

If it's expected to set a different process group then you can submit a PR (but ideally I'd like some answer to the questions above, especially if GNOME doesn't do it).

systemd-oomd works fine

[axelkar]

🤔 I'm not sure about this change, but systemd user services are run in separate process groups. I'll probably switch to oomd as it has cgroup support.

Is there any reason you didn't just do the spawning through the API behind systemd-run? (StartTransientUnit or something like that, but doing the actual execing in systemd)

[YaLTeR]

Don't want to wait for D-Bus before exec. Though admittedly I never profiled it so idk what the actual delay is

[axelkar]

Maybe you want to do something like this to get the PID to systemd: rust-lang/rust#113939

[YaLTeR]

I guess this is similar to what niri already does: it spawns an intermediate child process that spawns the final child, sends its PID back to the parent process, then waits till the parent process is done assigning this PID to a transient scope, and then exits.

The waiting part is annoying and causes #229. If pidfd would allow getting rid of waiting, it'd be good to switch to it. But I don't see StartTransientUnit accepting a pidfd?