Yeah, none of this makes sense to me. Allocating memory for stack space is not expensive (and the default isn't even 1MB??) because you're just creating a VMA and probably faulting in one or two pages.

They also say:

>The system spends time managing threads that could be better spent doing useful work.

What do they think the async runtime in their language is doing? It's literally doing the same thing the kernel would be doing. There's nothing that intrinsically makes scheduling 10k couroutines in userspace more efficient than the kernel scheduling 10k threads. Context switches are really only expensive when the switch is happening between different processes, the overhead of a context switch on a CPU between two threads in the same process is very small (and they're not free when done in userspace anyway).

There are advantages to doing scheduling in the kernel and there are advantages to doing scheduling in userspace, but this article doesn't really touch on any of the actual pros and cons here, it just assumes that userspace scheduling is automatically more efficient.

doesn't a async runtime have more knowledge about the tasks than the OS about the threads?

It's a cargo cult and a bias I see all over the place.

I feel like we're now, what, 20, 25 years on and people still haven't adjusted themselves to the fact that the machines we have now are multicore, have boatloads of cache, or how that cache is shared (or not) between cores.

Nor is there apparently a real understanding of the difference between VSS and RSS.

Nor of the fact that modern machines are really really fast if you can keep stuff in cache. And so you really should be focused on how you can make that happen.