If you allocate the stacks contiguously using mmap then memory is only used as it is accessed. That's not the problem. The problem is that 4000 concurrent non-t

If you allocate the stacks contiguously using mmap then memory is only used as it is accessed. That's not the problem. The problem is that 4000 concurrent non-trivial threads is a resource hog no matter how the stacks are allocated.