[PATCH v2] dm: Support turning off io stat accounting

[linan666]

From: Li Nan <linan122@xxxxxxxxxx>

Commit bc59ba9468d9 ("block: add sysfs file for controlling io stats
accounting") allowed user to turn off disk stat accounting completely by
queue flag QUEUE_FLAG_IO_STAT. In dm, this flag is not set for BIO_BASED
device, io stats is continuously counted and cannot be turn off.

Support turning off io stat accounting for dm. Set QUEUE_FLAG_IO_STAT for
dm request_queue. When the io starts, we account the io using DM_IO_STAT
dm_io flag to avoid io stats disable in the middle of the io. DM statistics
is independent of block io stat and remains unchanged.

Signed-off-by: Li Nan <linan122@xxxxxxxxxx>
---
v2:
 - set QUEUE_FLAG_IO_STAT in dm_setup_md_queue()
 - get request_queue by md->queue
---
 drivers/md/dm-core.h |  3 ++-
 drivers/md/dm.c      | 16 +++++++++++-----
 2 files changed, 13 insertions(+), 6 deletions(-)

diff --git a/drivers/md/dm-core.h b/drivers/md/dm-core.h
index aecab0c0720f..8b0af3e1331a 100644
--- a/drivers/md/dm-core.h
+++ b/drivers/md/dm-core.h
@@ -307,7 +307,8 @@ struct dm_io {
  */
 enum {
 	DM_IO_ACCOUNTED,
-	DM_IO_WAS_SPLIT
+	DM_IO_WAS_SPLIT,
+	DM_IO_STAT
 };
 
 static inline bool dm_io_flagged(struct dm_io *io, unsigned int bit)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 3b694ba3a106..fee27ae4129e 100644
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -511,11 +511,14 @@ static void dm_io_acct(struct dm_io *io, bool end)
 	else
 		sectors = io->sectors;
 
-	if (!end)
-		bdev_start_io_acct(bio->bi_bdev, bio_op(bio), start_time);
-	else
-		bdev_end_io_acct(bio->bi_bdev, bio_op(bio), sectors,
-				 start_time);
+	if (dm_io_flagged(io, DM_IO_STAT)) {
+		if (!end)
+			bdev_start_io_acct(bio->bi_bdev, bio_op(bio),
+					   start_time);
+		else
+			bdev_end_io_acct(bio->bi_bdev, bio_op(bio),
+					 sectors, start_time);
+	}
 
 	if (static_branch_unlikely(&stats_enabled) &&
 	    unlikely(dm_stats_used(&md->stats))) {
@@ -592,6 +595,8 @@ static struct dm_io *alloc_io(struct mapped_device *md, struct bio *bio)
 	spin_lock_init(&io->lock);
 	io->start_time = jiffies;
 	io->flags = 0;
+	if (blk_queue_io_stat(md->queue))
+		dm_io_set_flag(io, DM_IO_STAT);
 
 	if (static_branch_unlikely(&stats_enabled))
 		dm_stats_record_start(&md->stats, &io->stats_aux);
@@ -2341,6 +2346,7 @@ int dm_setup_md_queue(struct mapped_device *md, struct dm_table *t)
 		break;
 	case DM_TYPE_BIO_BASED:
 	case DM_TYPE_DAX_BIO_BASED:
+		blk_queue_flag_set(QUEUE_FLAG_IO_STAT, md->queue);
 		break;
 	case DM_TYPE_NONE:
 		WARN_ON_ONCE(true);
-- 
2.39.2