[PATCH 0/2] block/dm: add REQ_NOWAIT support for bio-based

[PATCH 0/2] block/dm: add REQ_NOWAIT support for bio-based

[Mike Snitzer]

Hi,

I got guilted into this by this Twitter exchange:
https://twitter.com/axboe/status/1308778488011337728

Started with this patchset from June and revised it:
https://patchwork.kernel.org/project/dm-devel/list/?series=297693
(dropped MD patch while doing so_.

Tested these changes with this test Jens provided:

[mikes-test-job]
filename=/dev/dm-0
rw=randread
buffered=1
ioengine=io_uring
iodepth=16
norandommap

Jens, please feel free to pickup both patches, I don't have any
conflicting DM changes for 5.10.

Thanks,
Mike

Konstantin Khlebnikov (1):
  dm: add support for REQ_NOWAIT and enable it for linear target

Mike Snitzer (1):
  block: add QUEUE_FLAG_NOWAIT

 block/blk-core.c              |  4 ++--
 drivers/md/dm-linear.c        |  5 +++--
 drivers/md/dm-table.c         | 32 ++++++++++++++++++++++++++++++++
 drivers/md/dm.c               |  4 +++-
 include/linux/blkdev.h        |  7 +++++--
 include/linux/device-mapper.h |  6 ++++++
 6 files changed, 51 insertions(+), 7 deletions(-)

-- 
2.15.0

[PATCH 1/2] block: add QUEUE_FLAG_NOWAIT

[Mike Snitzer]

Add QUEUE_FLAG_NOWAIT to allow a block device to advertise support for
REQ_NOWAIT. Bio-based devices may set QUEUE_FLAG_NOWAIT where
applicable.

Update QUEUE_FLAG_MQ_DEFAULT to include QUEUE_FLAG_NOWAIT.  Also
update submit_bio_checks() to verify it is set for REQ_NOWAIT bios.

Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Suggested-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 block/blk-core.c       | 4 ++--
 include/linux/blkdev.h | 7 +++++--
 2 files changed, 7 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index ca3f0f00c943..e3adfa135a20 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -817,9 +817,9 @@ static noinline_for_stack bool submit_bio_checks(struct bio *bio)
 
 	/*
 	 * For a REQ_NOWAIT based request, return -EOPNOTSUPP
-	 * if queue is not a request based queue.
+	 * if queue does not support NOWAIT.
 	 */
-	if ((bio->bi_opf & REQ_NOWAIT) && !queue_is_mq(q))
+	if ((bio->bi_opf & REQ_NOWAIT) && !blk_queue_nowait(q))
 		goto not_supported;
 
 	if (should_fail_bio(bio))
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index be5ef6f4ba19..9723b497d435 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -618,10 +618,12 @@ struct request_queue {
 #define QUEUE_FLAG_PCI_P2PDMA	25	/* device supports PCI p2p requests */
 #define QUEUE_FLAG_ZONE_RESETALL 26	/* supports Zone Reset All */
 #define QUEUE_FLAG_RQ_ALLOC_TIME 27	/* record rq->alloc_time_ns */
-#define QUEUE_FLAG_HCTX_ACTIVE 28	/* at least one blk-mq hctx is active */
+#define QUEUE_FLAG_HCTX_ACTIVE	28	/* at least one blk-mq hctx is active */
+#define QUEUE_FLAG_NOWAIT       29	/* device supports NOWAIT */
 
 #define QUEUE_FLAG_MQ_DEFAULT	((1 << QUEUE_FLAG_IO_STAT) |		\
-				 (1 << QUEUE_FLAG_SAME_COMP))
+				 (1 << QUEUE_FLAG_SAME_COMP) |		\
+				 (1 << QUEUE_FLAG_NOWAIT))
 
 void blk_queue_flag_set(unsigned int flag, struct request_queue *q);
 void blk_queue_flag_clear(unsigned int flag, struct request_queue *q);
@@ -661,6 +663,7 @@ bool blk_queue_flag_test_and_set(unsigned int flag, struct request_queue *q);
 #define blk_queue_pm_only(q)	atomic_read(&(q)->pm_only)
 #define blk_queue_fua(q)	test_bit(QUEUE_FLAG_FUA, &(q)->queue_flags)
 #define blk_queue_registered(q)	test_bit(QUEUE_FLAG_REGISTERED, &(q)->queue_flags)
+#define blk_queue_nowait(q)	test_bit(QUEUE_FLAG_NOWAIT, &(q)->queue_flags)
 
 extern void blk_set_pm_only(struct request_queue *q);
 extern void blk_clear_pm_only(struct request_queue *q);
-- 
2.15.0

[PATCH 2/2] dm: add support for REQ_NOWAIT and enable it for linear target

[Mike Snitzer]

From: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>

Add DM target feature flag DM_TARGET_NOWAIT which advertises that
target works with REQ_NOWAIT bios.

Add dm_table_supports_nowait() and update dm_table_set_restrictions()
to set/clear QUEUE_FLAG_NOWAIT accordingly.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
---
 drivers/md/dm-linear.c        |  5 +++--
 drivers/md/dm-table.c         | 32 ++++++++++++++++++++++++++++++++
 drivers/md/dm.c               |  4 +++-
 include/linux/device-mapper.h |  6 ++++++
 4 files changed, 44 insertions(+), 3 deletions(-)

diff --git a/drivers/md/dm-linear.c b/drivers/md/dm-linear.c
index e1db43446327..00774b5d7668 100644
--- a/drivers/md/dm-linear.c
+++ b/drivers/md/dm-linear.c
@@ -228,10 +228,11 @@ static struct target_type linear_target = {
 	.name   = "linear",
 	.version = {1, 4, 0},
 #ifdef CONFIG_BLK_DEV_ZONED
-	.features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_ZONED_HM,
+	.features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT |
+		    DM_TARGET_ZONED_HM,
 	.report_zones = linear_report_zones,
 #else
-	.features = DM_TARGET_PASSES_INTEGRITY,
+	.features = DM_TARGET_PASSES_INTEGRITY | DM_TARGET_NOWAIT,
 #endif
 	.module = THIS_MODULE,
 	.ctr    = linear_ctr,
diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
index acba92500c12..17fb9b96d18e 100644
--- a/drivers/md/dm-table.c
+++ b/drivers/md/dm-table.c
@@ -1719,6 +1719,33 @@ static bool dm_table_supports_write_zeroes(struct dm_table *t)
 	return true;
 }
 
+static int device_not_nowait_capable(struct dm_target *ti, struct dm_dev *dev,
+				     sector_t start, sector_t len, void *data)
+{
+	struct request_queue *q = bdev_get_queue(dev->bdev);
+
+	return q && !blk_queue_nowait(q);
+}
+
+static bool dm_table_supports_nowait(struct dm_table *t)
+{
+	struct dm_target *ti;
+	unsigned i = 0;
+
+	while (i < dm_table_get_num_targets(t)) {
+		ti = dm_table_get_target(t, i++);
+
+		if (!dm_target_supports_nowait(ti->type))
+			return false;
+
+		if (!ti->type->iterate_devices ||
+		    ti->type->iterate_devices(ti, device_not_nowait_capable, NULL))
+			return false;
+	}
+
+	return true;
+}
+
 static int device_not_discard_capable(struct dm_target *ti, struct dm_dev *dev,
 				      sector_t start, sector_t len, void *data)
 {
@@ -1821,6 +1848,11 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
 	 */
 	q->limits = *limits;
 
+	if (dm_table_supports_nowait(t))
+		blk_queue_flag_set(QUEUE_FLAG_NOWAIT, q);
+	else
+		blk_queue_flag_clear(QUEUE_FLAG_NOWAIT, q);
+
 	if (!dm_table_supports_discards(t)) {
 		blk_queue_flag_clear(QUEUE_FLAG_DISCARD, q);
 		/* Must also clear discard limits... */
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index b110b5eb99a5..3ad4a8da8b15 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1733,7 +1733,9 @@ static blk_qc_t dm_submit_bio(struct bio *bio)
 	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
 		dm_put_live_table(md, srcu_idx);
 
-		if (!(bio->bi_opf & REQ_RAHEAD))
+		if (bio->bi_opf & REQ_NOWAIT)
+			bio_wouldblock_error(bio);
+		else if (!(bio->bi_opf & REQ_RAHEAD))
 			queue_io(md, bio);
 		else
 			bio_io_error(bio);
diff --git a/include/linux/device-mapper.h b/include/linux/device-mapper.h
index 57610fc3013e..ba3b0979e09f 100644
--- a/include/linux/device-mapper.h
+++ b/include/linux/device-mapper.h
@@ -252,6 +252,12 @@ struct target_type {
 #define DM_TARGET_ZONED_HM		0x00000040
 #define dm_target_supports_zoned_hm(type) ((type)->features & DM_TARGET_ZONED_HM)
 
+/*
+ * A target handles REQ_NOWAIT
+ */
+#define DM_TARGET_NOWAIT		0x00000080
+#define dm_target_supports_nowait(type) ((type)->features & DM_TARGET_NOWAIT)
+
 struct dm_target {
 	struct dm_table *table;
 	struct target_type *type;
-- 
2.15.0

Re: [PATCH 1/2] block: add QUEUE_FLAG_NOWAIT

[Christoph Hellwig]

On Wed, Sep 23, 2020 at 04:06:51PM -0400, Mike Snitzer wrote:
> Add QUEUE_FLAG_NOWAIT to allow a block device to advertise support for
> REQ_NOWAIT. Bio-based devices may set QUEUE_FLAG_NOWAIT where
> applicable.
> 
> Update QUEUE_FLAG_MQ_DEFAULT to include QUEUE_FLAG_NOWAIT.  Also
> update submit_bio_checks() to verify it is set for REQ_NOWAIT bios.
> 
> Reported-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
> Suggested-by: Christoph Hellwig <hch@lst.de>
> Signed-off-by: Mike Snitzer <snitzer@redhat.com>

Looks good:

Reviewed-by: Christoph Hellwig <hch@lst.de>

Re: [PATCH 0/2] block/dm: add REQ_NOWAIT support for bio-based

[Jens Axboe]

On 9/23/20 2:06 PM, Mike Snitzer wrote:
> Hi,
> 
> I got guilted into this by this Twitter exchange:
> https://twitter.com/axboe/status/1308778488011337728
> 
> Started with this patchset from June and revised it:
> https://patchwork.kernel.org/project/dm-devel/list/?series=297693
> (dropped MD patch while doing so_.
> 
> Tested these changes with this test Jens provided:
> 
> [mikes-test-job]
> filename=/dev/dm-0
> rw=randread
> buffered=1
> ioengine=io_uring
> iodepth=16
> norandommap
> 
> Jens, please feel free to pickup both patches, I don't have any
> conflicting DM changes for 5.10.

Thanks Mike! Applied.

-- 
Jens Axboe