I've been googling for a while and the answers are unclear otherwise I wouldn't bother posting here.
In part because (for threads) it depends on the stack size you limit things to. For fds and sockets wanting more than 65k (especially per process, but per maybe per machine) is a very specialized thing.
Even this topic (on max threads) came to an uncertain resolution:
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lkml.org/lkml/2006/8/15/222
