stackless are regular coroutines except that there's 1 stack in the scheduler and when a coroutine yields, the current stack state is saved into the coroutine's

stackless are regular coroutines except that there's 1 stack in the scheduler and when a coroutine yields, the current stack state is saved into the coroutine's structure to be restored later. The disadvantage is that you'll need to copy out/in every time a coroutine yields. It's unrelated to gotos in a state machine. Having a stack per coroutine is not a big deal, especially if the coroutine library regularly advises the kernel on the memory areas it isn't using (madvise). What's stored on the stack usually needs to be stored somewhere else and ends up using a similar account of memory. When you allocate a 1MB stack per coroutine, the kernel will not wire it all to ram, but only the pages that have been touched. When the stack shrinks back and the coroutine yields, the scheduler can call madvise and inform the kernel that the no longer used pages from the 1MB can be reclaimed.