[PATCH v4 1/4] NFSD: avoid using iov_iter_is_aligned() in nfsd_iter_read()

[Mike Snitzer <snitzer@kernel.org>]

From: Mike Snitzer <snitzer@hammerspace.com>

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@hammerspace.com>
---
 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);
 	}
 
-- 
2.44.0