On Sat, Jan 23, 2021 at 07:41:39AM +0100, Christoph Hellwig wrote: > > In fact, I wonder if we need to do anything other than just use > > REQ_FUA unconditionally in iomap for this situation, as the block > > layer will translate REQ_FUA to a write+post-flush if the device > > doesn't support FUA writes directly. > > > > You're thoughts on that, Christoph? > > For the pure overwrite O_DIRECT + O_DSYNC case we'd get away with just > a flush. And using REQ_FUA will get us there, so it might be worth > a try. And looking at this a little more, while just using REQ_FUA would work it would be rather suboptimal for many cases, as the block layer flush state machine would do a flush for every bio. So for each O_DIRECT + O_DSYNC write that generates more than one bio we'd grow extra flushes.
