This is exactly what we do in Crystal: just mmap a new stack and let the OS deal with growing the stack through page faults. One thing I will say though is that you can't shrink the stack, which is a problem. You also may need to adjust vm.max_map_count to get more than 32k fibers.
> One thing I will say though is that you can't shrink the stack
It'd be manual but you could madvise it to shrink. Unlikely to be worth the effort unless you have one code flow that has a particularly deep stack vs. the common case, though.
