On Mon, May 21, 2018 at 09:16:33PM -0600, Jens Axboe wrote:

On 5/21/18 8:49 PM, Ming Lei wrote:

quoted

On Mon, May 21, 2018 at 05:11:31PM -0600, Keith Busch wrote:

quoted

This patch simplifies the timeout handling by relying on the request
reference counting to ensure the iterator is operating on an inflight

The reference counting isn't free, what is the real benefit in this way?

Neither is the current scheme and locking, and this is a hell of a lot
simpler. I'd get rid of the kref stuff and just do a simple
atomic_dec_and_test(). Most of the time we should be uncontended on
that, which would make it pretty darn cheap. I'd be surprised if it
wasn't better than the current alternatives.

The explicit memory barriers by atomic_dec_and_test() isn't free.

Also the double completion issue need to be fixed before discussing
this approach further.


Thanks,
Ming