I appreciate all your points. However, in my experience implementing coroutines and fibers, where I allocated stacks using `mmap`, with guard pages, I'm not completely convinced that fixed-size stacks are an issue:

1/ The typical C stack is fixed size and code is written accordingly.

2/ `mmap` can allocate virtual memory, so you can allocate a large stack but that's an upper limit, it might be paged out if unused.

Thoughts?