On Thu, Jul 24, 2025 at 09:28:39AM -0400, Chuck Lever wrote: > On 7/23/25 7:53 PM, 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. > > It sounds like we can't rely on clients to align the payload for NFSD. > So I'd say "we care". Not old or non-Linux clients, no... > Maybe NFSD could recognize when the content is already properly aligned > and take a shorter code path? I'm not familiar enough with your patches > yet to make a guess. Its pretty well optimized as-is, yes. So that isn't a major concern. I've just posted a rolled up v5 that keeps the NFSD capability, thanks for your guidance. Mike
