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. Let the NFS client do the lifting for us assessing how well NFSD's O_DIRECT works and yet have confidence that we can deploy support for old Linux clients or non-Linux clients in the future by merging that patch 5 (and NFSD misaligned WRITE support comparable to NFS's WRITE splitting in this series [1]) in a secondary phase. Good to have options. Mike [0]: https://lore.kernel.org/linux-nfs/20250723154351.59042-6-snitzer@xxxxxxxxxx/ [1]: https://lore.kernel.org/linux-nfs/20250722024924.49877-8-snitzer@xxxxxxxxxx/
