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Subject[PATCH 5.4 084/177] dm zoned: reduce overhead of backing device checks
Date
From: Dmitry Fomichev <dmitry.fomichev@wdc.com>

commit e7fad909b68aa37470d9f2d2731b5bec355ee5d6 upstream.

Commit 75d66ffb48efb3 added backing device health checks and as a part
of these checks, check_events() block ops template call is invoked in
dm-zoned mapping path as well as in reclaim and flush path. Calling
check_events() with ATA or SCSI backing devices introduces a blocking
scsi_test_unit_ready() call being made in sd_check_events(). Even though
the overhead of calling scsi_test_unit_ready() is small for ATA zoned
devices, it is much larger for SCSI and it affects performance in a very
negative way.

Fix this performance regression by executing check_events() only in case
of any I/O errors. The function dmz_bdev_is_dying() is modified to call
only blk_queue_dying(), while calls to check_events() are made in a new
helper function, dmz_check_bdev().

Reported-by: zhangxiaoxu <zhangxiaoxu5@huawei.com>
Fixes: 75d66ffb48efb3 ("dm zoned: properly handle backing device failure")
Cc: stable@vger.kernel.org
Signed-off-by: Dmitry Fomichev <dmitry.fomichev@wdc.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
drivers/md/dm-zoned-metadata.c | 29 ++++++++++++++--------
drivers/md/dm-zoned-reclaim.c | 8 +-----
drivers/md/dm-zoned-target.c | 54 ++++++++++++++++++++++++++++-------------
drivers/md/dm-zoned.h | 2 +
4 files changed, 61 insertions(+), 32 deletions(-)

--- a/drivers/md/dm-zoned-metadata.c
+++ b/drivers/md/dm-zoned-metadata.c
@@ -554,6 +554,7 @@ static struct dmz_mblock *dmz_get_mblock
TASK_UNINTERRUPTIBLE);
if (test_bit(DMZ_META_ERROR, &mblk->state)) {
dmz_release_mblock(zmd, mblk);
+ dmz_check_bdev(zmd->dev);
return ERR_PTR(-EIO);
}

@@ -625,6 +626,8 @@ static int dmz_rdwr_block(struct dmz_met
ret = submit_bio_wait(bio);
bio_put(bio);

+ if (ret)
+ dmz_check_bdev(zmd->dev);
return ret;
}

@@ -691,6 +694,7 @@ static int dmz_write_dirty_mblocks(struc
TASK_UNINTERRUPTIBLE);
if (test_bit(DMZ_META_ERROR, &mblk->state)) {
clear_bit(DMZ_META_ERROR, &mblk->state);
+ dmz_check_bdev(zmd->dev);
ret = -EIO;
}
nr_mblks_submitted--;
@@ -768,7 +772,7 @@ int dmz_flush_metadata(struct dmz_metada
/* If there are no dirty metadata blocks, just flush the device cache */
if (list_empty(&write_list)) {
ret = blkdev_issue_flush(zmd->dev->bdev, GFP_NOIO, NULL);
- goto out;
+ goto err;
}

/*
@@ -778,7 +782,7 @@ int dmz_flush_metadata(struct dmz_metada
*/
ret = dmz_log_dirty_mblocks(zmd, &write_list);
if (ret)
- goto out;
+ goto err;

/*
* The log is on disk. It is now safe to update in place
@@ -786,11 +790,11 @@ int dmz_flush_metadata(struct dmz_metada
*/
ret = dmz_write_dirty_mblocks(zmd, &write_list, zmd->mblk_primary);
if (ret)
- goto out;
+ goto err;

ret = dmz_write_sb(zmd, zmd->mblk_primary);
if (ret)
- goto out;
+ goto err;

while (!list_empty(&write_list)) {
mblk = list_first_entry(&write_list, struct dmz_mblock, link);
@@ -805,16 +809,20 @@ int dmz_flush_metadata(struct dmz_metada

zmd->sb_gen++;
out:
- if (ret && !list_empty(&write_list)) {
- spin_lock(&zmd->mblk_lock);
- list_splice(&write_list, &zmd->mblk_dirty_list);
- spin_unlock(&zmd->mblk_lock);
- }
-
dmz_unlock_flush(zmd);
up_write(&zmd->mblk_sem);

return ret;
+
+err:
+ if (!list_empty(&write_list)) {
+ spin_lock(&zmd->mblk_lock);
+ list_splice(&write_list, &zmd->mblk_dirty_list);
+ spin_unlock(&zmd->mblk_lock);
+ }
+ if (!dmz_check_bdev(zmd->dev))
+ ret = -EIO;
+ goto out;
}

/*
@@ -1244,6 +1252,7 @@ static int dmz_update_zone(struct dmz_me
if (ret) {
dmz_dev_err(zmd->dev, "Get zone %u report failed",
dmz_id(zmd, zone));
+ dmz_check_bdev(zmd->dev);
return ret;
}

--- a/drivers/md/dm-zoned-reclaim.c
+++ b/drivers/md/dm-zoned-reclaim.c
@@ -82,6 +82,7 @@ static int dmz_reclaim_align_wp(struct d
"Align zone %u wp %llu to %llu (wp+%u) blocks failed %d",
dmz_id(zmd, zone), (unsigned long long)wp_block,
(unsigned long long)block, nr_blocks, ret);
+ dmz_check_bdev(zrc->dev);
return ret;
}

@@ -489,12 +490,7 @@ static void dmz_reclaim_work(struct work
ret = dmz_do_reclaim(zrc);
if (ret) {
dmz_dev_debug(zrc->dev, "Reclaim error %d\n", ret);
- if (ret == -EIO)
- /*
- * LLD might be performing some error handling sequence
- * at the underlying device. To not interfere, do not
- * attempt to schedule the next reclaim run immediately.
- */
+ if (!dmz_check_bdev(zrc->dev))
return;
}

--- a/drivers/md/dm-zoned-target.c
+++ b/drivers/md/dm-zoned-target.c
@@ -80,6 +80,8 @@ static inline void dmz_bio_endio(struct

if (status != BLK_STS_OK && bio->bi_status == BLK_STS_OK)
bio->bi_status = status;
+ if (bio->bi_status != BLK_STS_OK)
+ bioctx->target->dev->flags |= DMZ_CHECK_BDEV;

if (refcount_dec_and_test(&bioctx->ref)) {
struct dm_zone *zone = bioctx->zone;
@@ -565,32 +567,52 @@ out:
}

/*
- * Check the backing device availability. If it's on the way out,
+ * Check if the backing device is being removed. If it's on the way out,
* start failing I/O. Reclaim and metadata components also call this
* function to cleanly abort operation in the event of such failure.
*/
bool dmz_bdev_is_dying(struct dmz_dev *dmz_dev)
{
- struct gendisk *disk;
+ if (dmz_dev->flags & DMZ_BDEV_DYING)
+ return true;

- if (!(dmz_dev->flags & DMZ_BDEV_DYING)) {
- disk = dmz_dev->bdev->bd_disk;
- if (blk_queue_dying(bdev_get_queue(dmz_dev->bdev))) {
- dmz_dev_warn(dmz_dev, "Backing device queue dying");
- dmz_dev->flags |= DMZ_BDEV_DYING;
- } else if (disk->fops->check_events) {
- if (disk->fops->check_events(disk, 0) &
- DISK_EVENT_MEDIA_CHANGE) {
- dmz_dev_warn(dmz_dev, "Backing device offline");
- dmz_dev->flags |= DMZ_BDEV_DYING;
- }
- }
+ if (dmz_dev->flags & DMZ_CHECK_BDEV)
+ return !dmz_check_bdev(dmz_dev);
+
+ if (blk_queue_dying(bdev_get_queue(dmz_dev->bdev))) {
+ dmz_dev_warn(dmz_dev, "Backing device queue dying");
+ dmz_dev->flags |= DMZ_BDEV_DYING;
}

return dmz_dev->flags & DMZ_BDEV_DYING;
}

/*
+ * Check the backing device availability. This detects such events as
+ * backing device going offline due to errors, media removals, etc.
+ * This check is less efficient than dmz_bdev_is_dying() and should
+ * only be performed as a part of error handling.
+ */
+bool dmz_check_bdev(struct dmz_dev *dmz_dev)
+{
+ struct gendisk *disk;
+
+ dmz_dev->flags &= ~DMZ_CHECK_BDEV;
+
+ if (dmz_bdev_is_dying(dmz_dev))
+ return false;
+
+ disk = dmz_dev->bdev->bd_disk;
+ if (disk->fops->check_events &&
+ disk->fops->check_events(disk, 0) & DISK_EVENT_MEDIA_CHANGE) {
+ dmz_dev_warn(dmz_dev, "Backing device offline");
+ dmz_dev->flags |= DMZ_BDEV_DYING;
+ }
+
+ return !(dmz_dev->flags & DMZ_BDEV_DYING);
+}
+
+/*
* Process a new BIO.
*/
static int dmz_map(struct dm_target *ti, struct bio *bio)
@@ -902,8 +924,8 @@ static int dmz_prepare_ioctl(struct dm_t
{
struct dmz_target *dmz = ti->private;

- if (dmz_bdev_is_dying(dmz->dev))
- return -ENODEV;
+ if (!dmz_check_bdev(dmz->dev))
+ return -EIO;

*bdev = dmz->dev->bdev;

--- a/drivers/md/dm-zoned.h
+++ b/drivers/md/dm-zoned.h
@@ -72,6 +72,7 @@ struct dmz_dev {

/* Device flags. */
#define DMZ_BDEV_DYING (1 << 0)
+#define DMZ_CHECK_BDEV (2 << 0)

/*
* Zone descriptor.
@@ -255,5 +256,6 @@ void dmz_schedule_reclaim(struct dmz_rec
* Functions defined in dm-zoned-target.c
*/
bool dmz_bdev_is_dying(struct dmz_dev *dmz_dev);
+bool dmz_check_bdev(struct dmz_dev *dmz_dev);

#endif /* DM_ZONED_H */

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