On 11/20/20 1:55 AM, Christoph Hellwig wrote:

quoted

quoted

diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..396ac0f91a43 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c

@@ -309,6 +309,16 @@ iomap_dio_bio_actor(struct inode *inode, loff_t pos, loff_t length,
  		copied += n;
  		nr_pages = iov_iter_npages(dio->submit.iter, BIO_MAX_PAGES);
+		/*
+		 * The current dio needs to be split into multiple bios here.
+		 * iopoll for split bio will cause subtle trouble such as
+		 * hang when doing sync polling, while iopoll is initially
+		 * for small size, latency sensitive IO. Thus disable iopoll
+		 * if split needed.
+		 */
+		if (nr_pages)
+			dio->iocb->ki_flags &= ~IOCB_HIPRI;

I think this is confusing two things.

Indeed there's two level of split concerning this issue when doing sync
iopoll.


The first is that one bio got split in block-core, and patch 1 of this patch
set just fixes this.


Second is that one dio got split into multiple bios in fs layer, and patch 2
fixes this.

quoted

  One is that we don't handle
polling well when there are multiple bios.  For this I think we should
only call bio_set_polled when we know there is a single bio.

How about the following patch:

--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c

@@ -60,12 +60,12 @@ int iomap_dio_iopoll(struct kiocb *kiocb, bool spin)

??EXPORT_SYMBOL_GPL(iomap_dio_iopoll);

??static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap
*iomap,
-???????????????????????????? struct bio *bio, loff_t pos)
+???????????????????????????? struct bio *bio, loff_t pos, bool split)