On Wed, Jul 23, 2025 at 07:53:04PM -0400, Mike Snitzer wrote: > On Wed, Jul 23, 2025 at 02:42:56PM -0400, Chuck Lever wrote: > > On 7/23/25 2:40 PM, Mike Snitzer wrote: > > > On Mon, Jul 21, 2025 at 10:49:17PM -0400, Mike Snitzer wrote: > > >> Hi, > > >> > > >> This "NFS DIRECT" series depends on the "NFSD DIRECT" series here: > > >> https://lore.kernel.org/linux-nfs/20250714224216.14329-1-snitzer@xxxxxxxxxx/ > > >> (for the benefit of nfsd_file_dio_alignment patch in this series) > > >> > > >> The first patch was posted as part of a LOCALIO revert series I posted > > >> a week or so ago, thankfully that series isn't needed thanks to Trond > > >> and Neil's efforts. BUT the first patch is needed, has Reviewed-by > > >> from Jeff and Neil and is marked for stable@. > > >> > > >> The biggest change in v2 is the introduction of O_DIRECT misaligned > > >> READ and WRITE handling for the benefit of LOCALIO. Please see patches > > >> 6 and 7 for more details. > > > > > > Turns out that these NFS client (fs/nfs/direct.c) changes that focused > > > on benefiting LOCALIO actually also benefit NFSD if/when it is > > > configured to use O_DIRECT [0]. > > > > > > Such that the NFS client's O_DIRECT code will split any misaligned > > > WRITE IO and NFSD will then happily issue the DIO-aligned "middle" of > > > a given misaligned WRITE IO down to the underlying filesystem. > > > > > > Same goes for READ, NFS client will expand the front of any misaligned > > > READ such that the bulk of the IO becomes DIO-aligned (only the final > > > partial tail page is misaligned). > > > > > > So with the NFS client changes in this series we actually don't _need_ > > > NFSD to have the same type of misaligned IO analysis and handling to > > > expand READs or split WRITEs to be DIO-aligned. Which reduces work > > > that NFSD needs to do by leaning on the NFS client having the > > > capability. > > > > I'm not quite following. Does that apply to non-Linux NFS clients too? > > No, old Linux clients without these changes or non-Linux clients > wouldn't have the capabilities offered (extending READs, splitting > WRITEs to be DIO-aligned). The question is: do we care? Long-term: > probably. > > I'd be fine with the NFSD DIRECT's misaligned IO support (READ already > implemented/posted [0], WRITE partially implemented but not posted) to > be land upstream so that we have the benefit of making the most of > NFSD's O_DIRECT support even if the client doesn't take steps to issue > IO that is DIO-aligned. > > Whichever way we go, it is potentially convenient that the less > "involved" NFSD DIRECT patch 5 [0] could be withheld initially. I meant to say: the _more_ involved NFSD DIRECT patch 5 ;) (that said, that really patch isn't so bad... but I do recall you hoping it cleaner, and that it'd need refinement in the future). > [0]: https://lore.kernel.org/linux-nfs/20250723154351.59042-6-snitzer@xxxxxxxxxx/
