On Fri, Oct 06, 2017 at 07:01:19AM -0500, Goldwyn Rodrigues wrote: > > > On 10/05/2017 12:19 PM, Shaohua Li wrote: > > On Wed, Oct 04, 2017 at 08:55:02AM -0500, Goldwyn Rodrigues wrote: > >> This is a continuation of the nowait support which was incorporated > >> a while back. We introduced REQ_NOWAIT which would return immediately > >> if the call would block at the block layer. Request based-devices > >> do not wait. However, bio based devices (the ones which exclusively > >> call make_request_fn) need to be trained to handle REQ_NOWAIT. > >> > >> This effort covers the devices under MD and DM which would block > >> for any reason. If there should be more devices or situations > >> which need to be covered, please let me know. > >> > >> The problem with partial writes discussed during v1 turned out > >> to be a bug in partial writes during direct I/O and is fixed > >> by the submitted patch[1]. > >> > >> Changes since v1: > >> - mddev to return early in case the device is suspended, within the md code as opposed to ->make_request() > >> - Check for nowait support with all the lower devices. Same with if adding a device which does not support nowait. > >> - Nowait under each raid is checked before the final I/O submission for the entire I/O. > >> > >> [1] https://patchwork.kernel.org/patch/9979887/ > > > > Does this fix the partial IO issue we discussed before? It looks not to me. The > > partial IO bailed out could be any part of an IO, so simply returning the > > successed size doesn't help. Am I missing anything? I didn't follow the > > discussion, maybe Jens knew. > > > > If the partial IO bailed out is any part of IO, isn't it supposed to > return the size of the IO succeeded _so far_? If a latter part of the IO > succeeds (with a failure in between) what are you supposed to return to > user in case of direct write()s? Would that even be correct in case it > is a file overwrite? I didn't argue about the return value. To me the partial IO issue can't be fixed simply by whatever 'return value'.
