Comment (by Roland Haas):

As of git hash 6576596 "wheeler: use makejobs" of simfactory2 most (all?) machines in simfactory support a -j switch on the level of simfactory making it easy for users to choose how many parallel make jobs to use.

It does not quite automatically pick the correct value but makes it straightforward to control this. Since -l seems to not really work and implementing locks will only allow per user limits (and not take into account activity of other users) and is typically fragile, I will close this as wontfix.

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Ticket URL: https://bitbucket.org/einsteintoolkit/tickets/issues/536/dont-overload-machines-while-building