[PATCH 0/4] block: improve iostat for md/bcache partitions

[PATCH 0/4] block: improve iostat for md/bcache partitions

[Song Liu]

Currently, devices like md, bcache uses disk_[start|end]_io_acct to report
iostat. These functions couldn't get proper iostat for partitions on these
devices.

This set resolves this issue by introducing part_[begin|end]_io_acct, and
using them in md and bcache code.

Song Liu (4):
  block: expose disk_map_sector_rcu() and hd_struct_put in genhd.h
  block: introduce part_[begin|end]_io_acct
  md: use part_[begin|end]_io_acct instead of disk_[begin|end]_io_acct
  bcache: use part_[begin|end]_io_acct instead of
    disk_[begin|end]_io_acct

 block/blk-core.c            | 20 ++++++++++++++++----
 block/blk.h                 |  8 --------
 block/genhd.c               |  1 +
 drivers/md/bcache/request.c | 14 ++++++++++----
 drivers/md/md.c             |  8 ++++++--
 include/linux/blkdev.h      |  5 +++++
 include/linux/genhd.h       |  8 ++++++++
 7 files changed, 46 insertions(+), 18 deletions(-)

--
2.24.1

[PATCH 1/4] block: expose disk_map_sector_rcu() and hd_struct_put in genhd.h

[Song Liu]

So they can be used in drivers.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 block/blk.h           | 8 --------
 block/genhd.c         | 1 +
 include/linux/genhd.h | 8 ++++++++
 3 files changed, 9 insertions(+), 8 deletions(-)

diff --git a/block/blk.h b/block/blk.h
index 94f7c084f68fc..a6bc909480111 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -332,8 +332,6 @@ void blk_queue_free_zone_bitmaps(struct request_queue *q);
 static inline void blk_queue_free_zone_bitmaps(struct request_queue *q) {}
 #endif
 
-struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector);
-
 int blk_alloc_devt(struct hd_struct *part, dev_t *devt);
 void blk_free_devt(dev_t devt);
 void blk_invalidate_devt(dev_t devt);
@@ -358,12 +356,6 @@ static inline int hd_struct_try_get(struct hd_struct *part)
 	return 1;
 }
 
-static inline void hd_struct_put(struct hd_struct *part)
-{
-	if (part->partno)
-		percpu_ref_put(&part->ref);
-}
-
 static inline void hd_free_part(struct hd_struct *part)
 {
 	free_percpu(part->dkstats);
diff --git a/block/genhd.c b/block/genhd.c
index 60ae4e1b4d387..5b9333317dcb4 100644
--- a/block/genhd.c
+++ b/block/genhd.c
@@ -349,6 +349,7 @@ struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector)
 	rcu_read_unlock();
 	return part;
 }
+EXPORT_SYMBOL_GPL(disk_map_sector_rcu);
 
 /**
  * disk_has_partitions
diff --git a/include/linux/genhd.h b/include/linux/genhd.h
index 31a54072ffd65..b47c64f9f26b4 100644
--- a/include/linux/genhd.h
+++ b/include/linux/genhd.h
@@ -380,6 +380,14 @@ void bd_set_size(struct block_device *bdev, loff_t size);
 int blkdev_ioctl(struct block_device *, fmode_t, unsigned, unsigned long);
 long compat_blkdev_ioctl(struct file *, unsigned, unsigned long);
 
+struct hd_struct *disk_map_sector_rcu(struct gendisk *disk, sector_t sector);
+
+static inline void hd_struct_put(struct hd_struct *part)
+{
+	if (part->partno)
+		percpu_ref_put(&part->ref);
+}
+
 #ifdef CONFIG_SYSFS
 int bd_link_disk_holder(struct block_device *bdev, struct gendisk *disk);
 void bd_unlink_disk_holder(struct block_device *bdev, struct gendisk *disk);
-- 
2.24.1

[PATCH 2/4] block: introduce part_[begin|end]_io_acct

[Song Liu]

These functions can be used to enable iostat for partitions on devices
like md, bcache.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 block/blk-core.c       | 20 ++++++++++++++++----
 include/linux/blkdev.h |  5 +++++
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/block/blk-core.c b/block/blk-core.c
index 93104c7470e8a..6603f56804f41 100644
--- a/block/blk-core.c
+++ b/block/blk-core.c
@@ -1455,10 +1455,9 @@ void blk_account_io_start(struct request *rq)
 	part_stat_unlock();
 }
 
-unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
+unsigned long part_start_io_acct(struct hd_struct *part, unsigned int sectors,
 		unsigned int op)
 {
-	struct hd_struct *part = &disk->part0;
 	const int sgrp = op_stat_group(op);
 	unsigned long now = READ_ONCE(jiffies);
 
@@ -1471,12 +1470,18 @@ unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
 
 	return now;
 }
+EXPORT_SYMBOL(part_start_io_acct);
+
+unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
+		unsigned int op)
+{
+	return part_start_io_acct(&disk->part0, sectors, op);
+}
 EXPORT_SYMBOL(disk_start_io_acct);
 
-void disk_end_io_acct(struct gendisk *disk, unsigned int op,
+void part_end_io_acct(struct hd_struct *part, unsigned int op,
 		unsigned long start_time)
 {
-	struct hd_struct *part = &disk->part0;
 	const int sgrp = op_stat_group(op);
 	unsigned long now = READ_ONCE(jiffies);
 	unsigned long duration = now - start_time;
@@ -1487,6 +1492,13 @@ void disk_end_io_acct(struct gendisk *disk, unsigned int op,
 	part_stat_local_dec(part, in_flight[op_is_write(op)]);
 	part_stat_unlock();
 }
+EXPORT_SYMBOL(part_end_io_acct);
+
+void disk_end_io_acct(struct gendisk *disk, unsigned int op,
+		unsigned long start_time)
+{
+	part_end_io_acct(&disk->part0, op, start_time);
+}
 EXPORT_SYMBOL(disk_end_io_acct);
 
 /*
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 285b59cfc0646..894e55c91e1d8 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -1931,6 +1931,11 @@ unsigned long disk_start_io_acct(struct gendisk *disk, unsigned int sectors,
 void disk_end_io_acct(struct gendisk *disk, unsigned int op,
 		unsigned long start_time);
 
+unsigned long part_start_io_acct(struct hd_struct *part, unsigned int sectors,
+		unsigned int op);
+void part_end_io_acct(struct hd_struct *part, unsigned int op,
+		unsigned long start_time);
+
 /**
  * bio_start_io_acct - start I/O accounting for bio based drivers
  * @bio:	bio to start account for
-- 
2.24.1

[PATCH 3/4] md: use part_[begin|end]_io_acct instead of disk_[begin|end]_io_acct

[Song Liu]

This enables proper statistics in /proc/diskstats for md partitions.

Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/md.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/drivers/md/md.c b/drivers/md/md.c
index 6b511c9007d38..00ca65b206d13 100644
--- a/drivers/md/md.c
+++ b/drivers/md/md.c
@@ -470,6 +470,7 @@ struct md_io {
 	bio_end_io_t *orig_bi_end_io;
 	void *orig_bi_private;
 	unsigned long start_time;
+	struct hd_struct *part;
 };
 
 static void md_end_io(struct bio *bio)
@@ -477,7 +478,8 @@ static void md_end_io(struct bio *bio)
 	struct md_io *md_io = bio->bi_private;
 	struct mddev *mddev = md_io->mddev;
 
-	disk_end_io_acct(mddev->gendisk, bio_op(bio), md_io->start_time);
+	part_end_io_acct(md_io->part, bio_op(bio), md_io->start_time);
+	hd_struct_put(md_io->part);
 
 	bio->bi_end_io = md_io->orig_bi_end_io;
 	bio->bi_private = md_io->orig_bi_private;
@@ -523,7 +525,9 @@ static blk_qc_t md_submit_bio(struct bio *bio)
 		bio->bi_end_io = md_end_io;
 		bio->bi_private = md_io;
 
-		md_io->start_time = disk_start_io_acct(mddev->gendisk,
+		md_io->part = disk_map_sector_rcu(mddev->gendisk,
+						  bio->bi_iter.bi_sector);
+		md_io->start_time = part_start_io_acct(md_io->part,
 						       bio_sectors(bio),
 						       bio_op(bio));
 	}
-- 
2.24.1

[PATCH 4/4] bcache: use part_[begin|end]_io_acct instead of disk_[begin|end]_io_acct

[Song Liu]

This enables proper statistics in /proc/diskstats for bcache partitions.

Cc: Coly Li <colyli@suse.de>
Signed-off-by: Song Liu <songliubraving@fb.com>
---
 drivers/md/bcache/request.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
index 7de82c67597ce..1d946f601f7eb 100644
--- a/drivers/md/bcache/request.c
+++ b/drivers/md/bcache/request.c
@@ -475,6 +475,7 @@ struct search {
 	unsigned int		read_dirty_data:1;
 	unsigned int		cache_missed:1;
 
+	struct hd_struct	*part;
 	unsigned long		start_time;
 
 	struct btree_op		op;
@@ -669,7 +670,8 @@ static void bio_complete(struct search *s)
 {
 	if (s->orig_bio) {
 		/* Count on bcache device */
-		disk_end_io_acct(s->d->disk, bio_op(s->orig_bio), s->start_time);
+		part_end_io_acct(s->part, bio_op(s->orig_bio), s->start_time);
+		hd_struct_put(s->part);
 
 		trace_bcache_request_end(s->d, s->orig_bio);
 		s->orig_bio->bi_status = s->iop.status;
@@ -731,7 +733,8 @@ static inline struct search *search_alloc(struct bio *bio,
 	s->write		= op_is_write(bio_op(bio));
 	s->read_dirty_data	= 0;
 	/* Count on the bcache device */
-	s->start_time		= disk_start_io_acct(d->disk, bio_sectors(bio), bio_op(bio));
+	s->part			= disk_map_sector_rcu(d->disk, bio->bi_iter.bi_sector);
+	s->start_time		= part_start_io_acct(s->part, bio_sectors(bio), bio_op(bio));
 	s->iop.c		= d->c;
 	s->iop.bio		= NULL;
 	s->iop.inode		= d->id;
@@ -1072,6 +1075,7 @@ struct detached_dev_io_private {
 	unsigned long		start_time;
 	bio_end_io_t		*bi_end_io;
 	void			*bi_private;
+	struct hd_struct	*part;
 };
 
 static void detached_dev_end_io(struct bio *bio)
@@ -1083,7 +1087,8 @@ static void detached_dev_end_io(struct bio *bio)
 	bio->bi_private = ddip->bi_private;
 
 	/* Count on the bcache device */
-	disk_end_io_acct(ddip->d->disk, bio_op(bio), ddip->start_time);
+	part_end_io_acct(ddip->part, bio_op(bio), ddip->start_time);
+	hd_struct_put(ddip->part);
 
 	if (bio->bi_status) {
 		struct cached_dev *dc = container_of(ddip->d,
@@ -1109,7 +1114,8 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio)
 	ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
 	ddip->d = d;
 	/* Count on the bcache device */
-	ddip->start_time = disk_start_io_acct(d->disk, bio_sectors(bio), bio_op(bio));
+	ddip->part = disk_map_sector_rcu(d->disk, bio->bi_iter.bi_sector);
+	ddip->start_time = part_start_io_acct(ddip->part, bio_sectors(bio), bio_op(bio));
 	ddip->bi_end_io = bio->bi_end_io;
 	ddip->bi_private = bio->bi_private;
 	bio->bi_end_io = detached_dev_end_io;
-- 
2.24.1

Re: [PATCH 4/4] bcache: use part_[begin|end]_io_acct instead of disk_[begin|end]_io_acct

[Coly Li]

On 2020/8/18 15:02, Song Liu wrote:
> This enables proper statistics in /proc/diskstats for bcache partitions.
> 
> Cc: Coly Li <colyli@suse.de>
> Signed-off-by: Song Liu <songliubraving@fb.com>

The code looks good to me. It is fine to submit this bcache patch in
your submission path.

Reviewed-by: Coly Li <colyli@suse.de>

Thanks.

Coly Li

> ---
>  drivers/md/bcache/request.c | 14 ++++++++++----
>  1 file changed, 10 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/md/bcache/request.c b/drivers/md/bcache/request.c
> index 7de82c67597ce..1d946f601f7eb 100644
> --- a/drivers/md/bcache/request.c
> +++ b/drivers/md/bcache/request.c
> @@ -475,6 +475,7 @@ struct search {
>  	unsigned int		read_dirty_data:1;
>  	unsigned int		cache_missed:1;
>  
> +	struct hd_struct	*part;
>  	unsigned long		start_time;
>  
>  	struct btree_op		op;
> @@ -669,7 +670,8 @@ static void bio_complete(struct search *s)
>  {
>  	if (s->orig_bio) {
>  		/* Count on bcache device */
> -		disk_end_io_acct(s->d->disk, bio_op(s->orig_bio), s->start_time);
> +		part_end_io_acct(s->part, bio_op(s->orig_bio), s->start_time);
> +		hd_struct_put(s->part);
>  
>  		trace_bcache_request_end(s->d, s->orig_bio);
>  		s->orig_bio->bi_status = s->iop.status;
> @@ -731,7 +733,8 @@ static inline struct search *search_alloc(struct bio *bio,
>  	s->write		= op_is_write(bio_op(bio));
>  	s->read_dirty_data	= 0;
>  	/* Count on the bcache device */
> -	s->start_time		= disk_start_io_acct(d->disk, bio_sectors(bio), bio_op(bio));
> +	s->part			= disk_map_sector_rcu(d->disk, bio->bi_iter.bi_sector);
> +	s->start_time		= part_start_io_acct(s->part, bio_sectors(bio), bio_op(bio));
>  	s->iop.c		= d->c;
>  	s->iop.bio		= NULL;
>  	s->iop.inode		= d->id;
> @@ -1072,6 +1075,7 @@ struct detached_dev_io_private {
>  	unsigned long		start_time;
>  	bio_end_io_t		*bi_end_io;
>  	void			*bi_private;
> +	struct hd_struct	*part;
>  };
>  
>  static void detached_dev_end_io(struct bio *bio)
> @@ -1083,7 +1087,8 @@ static void detached_dev_end_io(struct bio *bio)
>  	bio->bi_private = ddip->bi_private;
>  
>  	/* Count on the bcache device */
> -	disk_end_io_acct(ddip->d->disk, bio_op(bio), ddip->start_time);
> +	part_end_io_acct(ddip->part, bio_op(bio), ddip->start_time);
> +	hd_struct_put(ddip->part);
>  
>  	if (bio->bi_status) {
>  		struct cached_dev *dc = container_of(ddip->d,
> @@ -1109,7 +1114,8 @@ static void detached_dev_do_request(struct bcache_device *d, struct bio *bio)
>  	ddip = kzalloc(sizeof(struct detached_dev_io_private), GFP_NOIO);
>  	ddip->d = d;
>  	/* Count on the bcache device */
> -	ddip->start_time = disk_start_io_acct(d->disk, bio_sectors(bio), bio_op(bio));
> +	ddip->part = disk_map_sector_rcu(d->disk, bio->bi_iter.bi_sector);
> +	ddip->start_time = part_start_io_acct(ddip->part, bio_sectors(bio), bio_op(bio));
>  	ddip->bi_end_io = bio->bi_end_io;
>  	ddip->bi_private = bio->bi_private;
>  	bio->bi_end_io = detached_dev_end_io;
> 

Re: [PATCH 1/4] block: expose disk_map_sector_rcu() and hd_struct_put in genhd.h

[Christoph Hellwig]

On Tue, Aug 18, 2020 at 12:02:35AM -0700, Song Liu wrote:
> So they can be used in drivers.

Looking at your later patches I'd much rather hide the call to
disk_map_sector_rcu in the actual accounting helper.

Re: [PATCH 2/4] block: introduce part_[begin|end]_io_acct

[Christoph Hellwig]

On Tue, Aug 18, 2020 at 12:02:36AM -0700, Song Liu wrote:
> These functions can be used to enable iostat for partitions on devices
> like md, bcache.

Please follow a model like bio_start_io_acct - that is pass a bio
for all the input parameters except for the gendisk.  Given that we
don't have anywhere for the part to store that will need another
output paramater.

The end_io function should drop the hd_struct reference as well for
a well rounded API.