On Tue, Mar 15, 2022 at 1:29 PM Lennart Poettering <lennart@xxxxxxxxxxxxxx> wrote:
On Mo, 14.03.22 23:12, Felip Moll (felip@xxxxxxxxxxx) wrote:
> > But note that you can also run your main service as a service, and
> > then allocate a *single* scope unit for *all* your payloads.
>
> The main issue is the scope needs a pid attached to it. I thought that the
> scope could live without any process inside, but that's not happening.
> So every time a user step/job finishes, my main process must take care of
> it, and launch the scope again on the next coming job.
Leave a stub process around in it. i.e something similar to
"/bin/sleep infinity".
Ok.. this was my initial idea.
> The forked process just does the dbus call, and when the scope is ready it
> is moved to the corresponding cgroup (PIDFile=).
Hmm? PIDFile= is a property of *services*, not *scopes*.
Sorry I meant PIDs, not PIDFile of course.
And "scopes" cannot be moved to "cgroups". I cannot parse the above.
The forked process X does the dbus call to start the scope with PIDs=$(pidof X), and when the scope is ready,
X is moved into the scope cgroup.
Did you read up on scopes and services?
See https://systemd.io/CGROUP_DELEGATION/, it explains the concept of
"scopes". Scopes *have* cgroups, but cannot be moved to "cgroups".
Yes, it was a misunderstanding of my previous sentence.
> Problem number one: if other processes are in the scope, the dbus call
> won't work since I am using the same name all the time, e.g.
> slurmstepd.scope.
> So I first need to check if the scope exists and if so put the new
> slurmstepd process inside. But we still have the race condition, if during
> this phase all steps ends, systemd will do the cleanup.
Leave a stub process around in it.
Ok, then I don't see the real difference of starting up a new service.
> If instead I could just ask systemd to delegate a part of the tree for my
> processes, then everything would be solved.
I don't follow. You can enable delegation on the scope. I mean, that's
the reason I suggested to use a scope.
Meaning that it would be great to have a delegated cgroup subtree without the need of a service or scope.
Just an empty subtree.
> Do you have any other suggestions?
Not really, except maybe: please read up on the documentation, it
explains a lot of the concepts.
I've done, I may not be expressing myself perfectly though. I apologize for that.
