On Wed, Aug 06, 2025 at 09:18:51AM -0400, Chuck Lever wrote:
> On 8/5/25 2:44 PM, Mike Snitzer wrote:
> > From: Mike Snitzer <snitzer@xxxxxxxxxxxxxxx>
> >
> > Check the bvec is DIO-aligned while creating it, saves CPU cycles by
> > avoiding iterating the bvec elements a second time using
> > iov_iter_is_aligned().
> >
> > This prepares for Keith Busch's near-term removal of the
> > iov_iter_is_aligned() interface. This fixes cel/nfsd-testing commit
> > 5d78ac1e674b4 ("NFSD: issue READs using O_DIRECT even if IO is
> > misaligned") and it should be folded into that commit so that NFSD
> > doesn't require iov_iter_is_aligned() while it is being removed
> > upstream in parallel.
> >
> > Fixes: cel/nfsd-testing 5d78ac1e674b4 ("NFSD: issue READs using O_DIRECT even if IO is misaligned")
> > Signed-off-by: Mike Snitzer <snitzer@xxxxxxxxxxxxxxx>
> > ---
> > fs/nfsd/vfs.c | 29 +++++++++++++++--------------
> > 1 file changed, 15 insertions(+), 14 deletions(-)
> >
> > diff --git a/fs/nfsd/vfs.c b/fs/nfsd/vfs.c
> > index 46189020172fb..e1751d3715264 100644
> > --- a/fs/nfsd/vfs.c
> > +++ b/fs/nfsd/vfs.c
> > @@ -1226,7 +1226,10 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > */
> > offset = read_dio.start;
> > in_count = read_dio.end - offset;
> > - kiocb.ki_flags = IOCB_DIRECT;
> > + /* Verify ondisk DIO alignment, memory addrs checked below */
> > + if (likely(((offset | in_count) &
> > + (nf->nf_dio_read_offset_align - 1)) == 0))
> > + kiocb.ki_flags = IOCB_DIRECT;
> > }
> > } else if (nfsd_io_cache_read == NFSD_IO_DONTCACHE)
> > kiocb.ki_flags = IOCB_DONTCACHE;
> > @@ -1236,16 +1239,24 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > v = 0;
> > total = in_count;
> > if (read_dio.start_extra) {
> > - bvec_set_page(&rqstp->rq_bvec[v++], read_dio.start_extra_page,
> > + bvec_set_page(&rqstp->rq_bvec[v], read_dio.start_extra_page,
> > read_dio.start_extra, PAGE_SIZE - read_dio.start_extra);
> > + if (unlikely((kiocb.ki_flags & IOCB_DIRECT) &&
> > + rqstp->rq_bvec[v].bv_offset & (nf->nf_dio_mem_align - 1)))
> > + kiocb.ki_flags &= ~IOCB_DIRECT;
> > total -= read_dio.start_extra;
> > + v++;
> > }
> > while (total) {
> > len = min_t(size_t, total, PAGE_SIZE - base);
> > - bvec_set_page(&rqstp->rq_bvec[v++], *(rqstp->rq_next_page++),
> > - len, base);
> > + bvec_set_page(&rqstp->rq_bvec[v], *(rqstp->rq_next_page++), len, base);
> > + /* No need to verify memory is DIO-aligned since bv_offset is 0 */
> > + if (unlikely((kiocb.ki_flags & IOCB_DIRECT) && base &&
> > + (base & (nf->nf_dio_mem_align - 1))))
> > + kiocb.ki_flags &= ~IOCB_DIRECT;
> > total -= len;
> > base = 0;
> > + v++;
> > }
> > if (WARN_ONCE(v > rqstp->rq_maxpages,
> > "%s: v=%lu exceeds rqstp->rq_maxpages=%lu\n", __func__,
> > @@ -1256,16 +1267,6 @@ __be32 nfsd_iter_read(struct svc_rqst *rqstp, struct svc_fh *fhp,
> > if (!host_err) {
> > trace_nfsd_read_vector(rqstp, fhp, offset, in_count);
> > iov_iter_bvec(&iter, ITER_DEST, rqstp->rq_bvec, v, in_count);
> > -
> > - /* Double check nfsd_analyze_read_dio's DIO-aligned result */
> > - if (unlikely((kiocb.ki_flags & IOCB_DIRECT) &&
> > - !iov_iter_is_aligned(&iter,
> > - nf->nf_dio_mem_align - 1,
> > - nf->nf_dio_read_offset_align - 1))) {
> > - /* Fallback to buffered IO */
> > - kiocb.ki_flags &= ~IOCB_DIRECT;
> > - }
> > -
> > host_err = vfs_iocb_iter_read(file, &kiocb, &iter);
> > }
> >
>
> Hi Mike,
>
> In cases where the SQUASHME patch is this large, I usually drop the
> patch (or series) in nfsd-testing and ask the contributor to rebase and
> repost. This gets the new version of the patch properly archived on
> lore, for one thing.
Yeah, make sense, I missed that iov_iter_is_aligned() was used early
on in the series too, so I'll fixup further back.
> Before reposting, please do run checkpatch.pl on the series.
Will do, will also ensure bisect safe and that sparse is happy.
Thanks,
Mike
