io_pgetevents & aio fsync V3

Hi all, this patch adds workqueue based fsync offload. Version of this patch have been floating around for a couple years, but we now have a user with seastar used by ScyllaDB (who sponsored this work) that really wants this in addition to the aio poll support. More details are in the patch

io_pgetevents & aio fsync V3

Hi all, this patch adds workqueue based fsync offload. Version of this patch have been floating around for a couple years, but we now have a user with seastar used by ScyllaDB (who sponsored this work) that really wants this in addition to the aio poll support. More details are in the patch