On 11/23/20 4:45 PM, Hao Xu wrote:
Currently, IOCB_NOWAIT is ignored in Direct IO, REQ_NOWAIT is only set
when IOCB_HIPRI is set. But REQ_NOWAIT should be set as well when
IOCB_NOWAIT is set.
Suggested-by: Jeffle Xu <jefflexu@xxxxxxxxxxxxxxxxx>
Signed-off-by: Konstantin Khlebnikov <khlebnikov@xxxxxxxxxxxxxx>
Signed-off-by: Hao Xu <haoxu@xxxxxxxxxxxxxxxxx>
---
Hi all,
I tested fio io_uring direct read for a file on ext4 filesystem on a
nvme ssd. I found that IOCB_NOWAIT is ignored in iomap layer, which
means REQ_NOWAIT is not set in bio->bi_opf. This makes nowait IO a
normal IO. Since I'm new to iomap and block layer, I sincerely ask
yours opinions in case I misunderstand the code which is very likely
to happen.:)
I found that Konstantin found this issue before in May
2020 (https://www.spinics.net/lists/linux-block/msg53275.html), here add
his signature, add Jeffle's as well since he gave me some help.
v1->v2:
* add same logic in __blkdev_direct_IO_simple()
v2->v3:
* add same logic in do_blockdev_direct_IO()
fs/block_dev.c | 7 +++++++
fs/direct-io.c | 6 ++++--
fs/iomap/direct-io.c | 3 +++
3 files changed, 14 insertions(+), 2 deletions(-)
diff --git a/fs/block_dev.c b/fs/block_dev.c
index 9e84b1928b94..f3e9e13a9a9f 100644
--- a/fs/block_dev.c
+++ b/fs/block_dev.c
@@ -263,6 +263,10 @@ static void blkdev_bio_end_io_simple(struct bio *bio)
bio.bi_opf = dio_bio_write_op(iocb);
task_io_account_write(ret);
}
+
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ bio.bi_opf |= REQ_NOWAIT;
+
if (iocb->ki_flags & IOCB_HIPRI)
bio_set_polled(&bio, iocb);
@@ -424,6 +428,9 @@ static void blkdev_bio_end_io(struct bio *bio)
if (!nr_pages) {
bool polled = false;
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ bio->bi_opf |= REQ_NOWAIT;
+
This should be moved outside the "if (!nr_pages) {}" clause. One direct
IO can be split
into several bios, among which only the last split bio will get into
this conditional clause.
Thanks,
Jeffle
if (iocb->ki_flags & IOCB_HIPRI) {
bio_set_polled(bio, iocb);
polled = true;
diff --git a/fs/direct-io.c b/fs/direct-io.c
index d53fa92a1ab6..b221ed351c1c 100644
--- a/fs/direct-io.c
+++ b/fs/direct-io.c
@@ -1206,11 +1206,13 @@ static inline int drop_refcount(struct dio *dio)
if (iov_iter_rw(iter) == WRITE) {
dio->op = REQ_OP_WRITE;
dio->op_flags = REQ_SYNC | REQ_IDLE;
- if (iocb->ki_flags & IOCB_NOWAIT)
- dio->op_flags |= REQ_NOWAIT;
} else {
dio->op = REQ_OP_READ;
}
+
+ if (iocb->ki_flags & IOCB_NOWAIT)
+ dio->op_flags |= REQ_NOWAIT;
+
if (iocb->ki_flags & IOCB_HIPRI)
dio->op_flags |= REQ_HIPRI;
diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
index 933f234d5bec..2e897688ed6d 100644
--- a/fs/iomap/direct-io.c
+++ b/fs/iomap/direct-io.c
@@ -64,6 +64,9 @@ static void iomap_dio_submit_bio(struct iomap_dio *dio, struct iomap *iomap,
{
atomic_inc(&dio->ref);
+ if (dio->iocb->ki_flags & IOCB_NOWAIT)
+ bio->bi_opf |= REQ_NOWAIT;
+
if (dio->iocb->ki_flags & IOCB_HIPRI)
bio_set_polled(bio, dio->iocb);
--
Thanks,
Jeffle
