What makes you think this should work?

This key is not documented in https://specifications.freedesktop.org/desktop-entry-spec/latest/recognized-keys.html or https://systemd.io/DESKTOP_ENVIRONMENTS/

Is this documented somewhere else?

(In reply to Nicolas Fella from comment #1)
> What makes you think this should work?
> 
> This key is not documented in
> https://specifications.freedesktop.org/desktop-entry-spec/latest/recognized-
> keys.html or https://systemd.io/DESKTOP_ENVIRONMENTS/
> 
> Is this documented somewhere else?

OMG you are right! [one can skip the background story] Yesterday I tried to use ChatGPT to setup ressource management with systemd, to assign applications like Kdenlive or Kdevelop to intense.slice. ChatGPT suggested to use the desktop entry SystemdSlice, but told me that this option is not widely used because "Desktop Environments only recently began to integrate more tightly with systemd". GPT suggested to look deeper into the source code of Gnome, KDE or systemd to find more information about this option. I think it is another case of ChatGPT hallucinating. But the hallucination is probably not that bad. Because user slices under user.slice can be used to assign applications for more fine-grained ressource management. Maybe extended functionality with KDE Menu Editor could be useful for this purpose.

Long story short, I have to do source code research to find if ChatGPT was hallucinating/envisioning or not.

Does anyone think SystemdSlice entry could be useful?

INFO:

For now I use this:
Exec=systemd-run --user --slice=intense.slice kdevelop

with my custom desktop file.

Additional coding fun fact:
I've set my PATH environment to "/home/me/bin:/usr/bin" and put the following make-wrapper into `/home/me/bin`:
--
#!/bin/bash

# Check if the script is being run as root
if [ "$EUID" -eq 0 ]; then
    # Run make within a systemd slice with --pipe to pass output directly
    systemd-run --quiet --same-dir --slice=build.slice --wait --pipe /bin/make "$@"
else
    # Run the command normally if already in user context
    systemd-run --quiet --same-dir --user --slice=build.slice --wait --pipe /bin/make "$@"
fi
--
now my 12 core workhorse system is perfectly balanced. Heavy build jobs run in a build.slice which forbids swap usage.
app.slice and intense.slice run perfectly smooth and responsive with high cpu priority on swap during builds now.

This kind of resource management is more powerful than expected.

INFO:

Additional update on the demo wrapper script `/home/me/bin/make` mentioned below. This version also terminates the process inside the build.slice as the script is terminated by kdevelop for example:
--
#!/bin/bash

# Run the command in the systemd slice and capture job ID
# Check if the script is being run as root
if [ "$EUID" -eq 0 ]; then
    # Run make within a systemd slice with --pipe to pass output directly
    systemd-run --same-dir --scope --send-sighup --quiet --slice=build.slice /bin/make "$@"
else
    # Run the command normally if already in user context
    systemd-run --user --same-dir --scope --quiet --send-sighup --slice=build.slice /bin/make "$@"
fi
--

INFO:

Update on my current workaround. --scope option is of course needed:
Exec=systemd-run --user --scope --slice=intense.slice kdevelop

See this blog post to set resource limits for specific apps https://blogs.kde.org/2024/10/18/limit-application-memory-usage-with-systemd/