On Thu, Aug 03, 2017 at 10:05:44AM +0200, Christoph Hellwig wrote: > FYI, for the read side we should use the on-stack bio unconditionally, > as it will always be a win (or not show up at all).
Think about readahead. Unconditional on-stack bio to read around pages with faulted address will cause latency peek. So, I want to use that synchronous IO only if device says "Hey, I'm a synchronous".
