Not if we decouple the ringbuffer size from max_requests.

Hmm, interesting.

This would be useful to do anyways because right now, allocating a kiocb
has to take a global refcount and check head and tail in the ringbuffer
just so it can avoid overflowing the ringbuffer.

I'm not sure what you mean by a 'global refcount'.. do you mean the
per-mm ctx_lock?

If we change aio_complete() so that if the ringbuffer is full then the
kiocb just goes on a linked list - we can size the ringbuffer so this
doesn't happen normally and avoid the global synchronization in the fast
path.

How would completion events make their way from the list to the ring if
an app is only checking the ring for completions from userspace?

- z