[simonask]

There isn’t any operating system or compiler that does this today, and it probably isn’t worth it to pursue. Enlarging the stack via page fault is really expensive, so you would need really advanced heuristics to prevent repeatedly unmapping/remapping those pages.

The correct tool for myriad of small tasks is coroutines / green threads / async tasks, so why spend any energy optimizing threads for that purpose instead of what they are already good at?

[dwattttt]

In the general case it's absolutely not worth it. In the context of "you want a large number of OS threads, and are willing to go to some effort", it's theoretically something you'd want to do; suppose the startup for a thread is measurably a high water mark for stack usage, after startup the steady state stack usage won't exceed 20% of that high mark, and you'd like as many threads/stacks as possible.

Coroutines / green threads / async tasks will all do this too, but there's something to be said for using/relying on the system scheduler instead of bringing your own in in addition.