Comment # 17 on bug 965564 from Thomas Blume

(In reply to Ludwig Nussel from comment #15)
> (In reply to Thomas Blume from comment #13)
> > systemd 228 has these defaults (/etc/systemd/system.conf):
> > 
> > #DefaultTasksMax=512
> > 
> > I guess this is the bottleneck.
> > Can't you just set it to a higher value for the build machines?
> 
> Still feels like a workaround. Shouldn't systemd clean up after itself and
> undo the changes it did to cgroups?

Hm, systemd only resets RLIMIT_NOFILE at reexecute:

-->--
                /* Reset the RLIMIT_NOFILE to the kernel default, so
                 * that the new systemd can pass the kernel default to
                 * its child processes */
                if (saved_rlimit_nofile.rlim_cur > 0)
                        (void) setrlimit(RLIMIT_NOFILE, &saved_rlimit_nofile);
--<--

Maybe it should also reset RLIMIT_NPROC?

But I'm unsure wheter this would have an effect on the reported behaviour,
unless:

DefaultTasksAccounting=no

is set in system.conf. See the systemd.resource-control manpage for details.