On Fri, Aug 14, 2020 at 08:27:13AM +0000, Damien Le Moal wrote: > > > > O_APPEND pretty much implies out of order, as there is no way for an > > application to know which thread wins the race to write the next chunk. > > Yes and no. If the application threads do not synchronize their calls to > io_submit(), then yes indeed, things can get out of order. But if the > application threads are synchronized, then the offset set for each append AIO > will be in sequence of submission, so the user will not see its writes > completing at different write offsets than this implied offsets. Nothing gurantees any kind of ordering for two separate io_submit calls. The kernel may delay one of them for any reason. Now if you are doing two fully synchronous write calls on an O_APPEND fd, yes they are serialized. But using Zone Append won't change that.
