[PATCH 3/3] iomap: use filemap_range_needs_writeback() for O_DIRECT reads

[Jens Axboe <axboe@kernel.dk>]

For reads, use the better variant of checking for the need to call
filemap_write_and_wait_range() when doing O_DIRECT. This avoids falling
back to the slow path for IOCB_NOWAIT, if there are no pages to wait for
(or write out).

Signed-off-by: Jens Axboe <axboe@kernel.dk>
---
 fs/iomap/direct-io.c | 23 +++++++++++++++--------
 1 file changed, 15 insertions(+), 8 deletions(-)

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..5b111d1635ab 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -458,9 +458,24 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 		if (pos >= dio->i_size)
 			goto out_free_dio;
 
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			if (filemap_range_needs_writeback(mapping, pos, end)) {
+				ret = -EAGAIN;
+				goto out_free_dio;
+			}
+			flags |= IOMAP_NOWAIT;
+		}
 		if (iter_is_iovec(iter))
 			dio->flags |= IOMAP_DIO_DIRTY;
 	} else {
+		if (iocb->ki_flags & IOCB_NOWAIT) {
+			if (filemap_range_has_page(mapping, pos, end)) {
+				ret = -EAGAIN;
+				goto out_free_dio;
+			}
+			flags |= IOMAP_NOWAIT;
+		}
+
 		flags |= IOMAP_WRITE;
 		dio->flags |= IOMAP_DIO_WRITE;
 
@@ -478,14 +493,6 @@ __iomap_dio_rw(struct kiocb *iocb, struct iov_iter *iter,
 			dio->flags |= IOMAP_DIO_WRITE_FUA;
 	}
 
-	if (iocb->ki_flags & IOCB_NOWAIT) {
-		if (filemap_range_has_page(mapping, pos, end)) {
-			ret = -EAGAIN;
-			goto out_free_dio;
-		}
-		flags |= IOMAP_NOWAIT;
-	}
-
 	ret = filemap_write_and_wait_range(mapping, pos, end);
 	if (ret)
 		goto out_free_dio;
-- 
2.30.0