dm-devel.redhat.com archive mirror
 help / color / mirror / Atom feed
From: JeffleXu <jefflexu@linux.alibaba.com>
To: Ming Lei <ming.lei@redhat.com>, Jens Axboe <axboe@kernel.dk>,
	Mike Snitzer <snitzer@redhat.com>
Cc: linux-block@vger.kernel.org, dm-devel@redhat.com,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [dm-devel] [RFC PATCH V2 3/3] dm: support bio polling
Date: Fri, 18 Jun 2021 16:19:10 +0800	[thread overview]
Message-ID: <5ba43dac-b960-7c85-3a89-fdae2d1e2f51@linux.alibaba.com> (raw)
In-Reply-To: <20210617103549.930311-4-ming.lei@redhat.com>



On 6/17/21 6:35 PM, Ming Lei wrote:
> Support bio(REQ_POLLED) polling in the following approach:
> 
> 1) only support io polling on normal READ/WRITE, and other abnormal IOs
> still fallback on IRQ mode, so the target io is exactly inside the dm
> io.
> 
> 2) hold one refcnt on io->io_count after submitting this dm bio with
> REQ_POLLED
> 
> 3) support dm native bio splitting, any dm io instance associated with
> current bio will be added into one list which head is bio->bi_end_io
> which will be recovered before ending this bio
> 
> 4) implement .poll_bio() callback, call bio_poll() on the single target
> bio inside the dm io which is retrieved via bio->bi_bio_drv_data; call
> dec_pending() after the target io is done in .poll_bio()
> 
> 4) enable QUEUE_FLAG_POLL if all underlying queues enable QUEUE_FLAG_POLL,
> which is based on Jeffle's previous patch.
> 
> Signed-off-by: Ming Lei <ming.lei@redhat.com>
> ---
>  drivers/md/dm-table.c |  24 +++++++++
>  drivers/md/dm.c       | 111 ++++++++++++++++++++++++++++++++++++++++--
>  2 files changed, 132 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/md/dm-table.c b/drivers/md/dm-table.c
> index ee47a332b462..b14b379442d2 100644
> --- a/drivers/md/dm-table.c
> +++ b/drivers/md/dm-table.c
> @@ -1491,6 +1491,12 @@ struct dm_target *dm_table_find_target(struct dm_table *t, sector_t sector)
>  	return &t->targets[(KEYS_PER_NODE * n) + k];
>  }
>  
> +static int device_not_poll_capable(struct dm_target *ti, struct dm_dev *dev,
> +				   sector_t start, sector_t len, void *data)
> +{
> +	return !blk_queue_poll(bdev_get_queue(dev->bdev));
> +}
> +
>  /*
>   * type->iterate_devices() should be called when the sanity check needs to
>   * iterate and check all underlying data devices. iterate_devices() will
> @@ -1541,6 +1547,11 @@ static int count_device(struct dm_target *ti, struct dm_dev *dev,
>  	return 0;
>  }
>  
> +static int dm_table_supports_poll(struct dm_table *t)
> +{
> +	return !dm_table_any_dev_attr(t, device_not_poll_capable, NULL);
> +}
> +
>  /*
>   * Check whether a table has no data devices attached using each
>   * target's iterate_devices method.
> @@ -2078,6 +2089,19 @@ void dm_table_set_restrictions(struct dm_table *t, struct request_queue *q,
>  
>  	dm_update_keyslot_manager(q, t);
>  	blk_queue_update_readahead(q);
> +
> +	/*
> +	 * Check for request-based device is remained to
> +	 * dm_mq_init_request_queue()->blk_mq_init_allocated_queue().
> +	 * For bio-based device, only set QUEUE_FLAG_POLL when all underlying
> +	 * devices supporting polling.
> +	 */
> +	if (__table_type_bio_based(t->type)) {
> +		if (dm_table_supports_poll(t))
> +			blk_queue_flag_set(QUEUE_FLAG_POLL, q);
> +		else
> +			blk_queue_flag_clear(QUEUE_FLAG_POLL, q);
> +	}
>  }
>  
>  unsigned int dm_table_get_num_targets(struct dm_table *t)
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index 363f12a285ce..9745c3deacc3 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -39,6 +39,8 @@
>  #define DM_COOKIE_ENV_VAR_NAME "DM_COOKIE"
>  #define DM_COOKIE_LENGTH 24
>  
> +#define REQ_SAVED_END_IO             REQ_DRV
> +
>  static const char *_name = DM_NAME;
>  
>  static unsigned int major = 0;
> @@ -97,8 +99,11 @@ struct dm_io {
>  	unsigned magic;
>  	struct mapped_device *md;
>  	blk_status_t status;
> +	bool	submit_as_polled;
>  	atomic_t io_count;
>  	struct bio *orig_bio;
> +	void	*saved_bio_end_io;
> +	struct hlist_node  node;
>  	unsigned long start_time;
>  	spinlock_t endio_lock;
>  	struct dm_stats_aux stats_aux;
> @@ -687,6 +692,8 @@ static struct dm_target_io *alloc_tio(struct clone_info *ci, struct dm_target *t
>  	tio->ti = ti;
>  	tio->target_bio_nr = target_bio_nr;
>  
> +	WARN_ON_ONCE(ci->io->submit_as_polled && !tio->inside_dm_io);
> +
>  	return tio;
>  }
>  
> @@ -938,8 +945,12 @@ static void dec_pending(struct dm_io *io, blk_status_t error)
>  		end_io_acct(io);
>  		free_io(md, io);
>  
> -		if (io_error == BLK_STS_DM_REQUEUE)
> +		if (io_error == BLK_STS_DM_REQUEUE) {
> +			/* not poll any more in case of requeue */
> +			if (bio->bi_opf & REQ_POLLED)
> +				bio->bi_opf &= ~REQ_POLLED;
>  			return;
> +		}

Actually I'm not sure why REQ_POLLED should be cleared here.

Besides, there's one corner case where bio is submitted when dm device
is suspended.

```
static blk_qc_t dm_submit_bio(struct bio *bio)

	/* If suspended, queue this IO for later */
	if (unlikely(test_bit(DMF_BLOCK_IO_FOR_SUSPEND, &md->flags))) {
		if (bio->bi_opf & REQ_NOWAIT)
			bio_wouldblock_error(bio);
		else if (bio->bi_opf & REQ_RAHEAD)
			bio_io_error(bio);
		else
			queue_io(md, bio);
		goto out;
	}
```

When the dm device is suspended with DMF_BLOCK_IO_FOR_SUSPEND, the
submitted bio is inserted into @md->deferred list by calling queue_io().
Then the following bio_poll() calling will trigger the
'WARN_ON_ONCE(!saved_bi_end_io)' in dm_poll_bio(), if the previously
submitted bio is still buffered in @md->deferred list.

```
submit_bio()
  dm_submit_bio
    queue_io

bio_poll
  dm_poll_bio
```


>  
>  		if ((bio->bi_opf & REQ_PREFLUSH) && bio->bi_iter.bi_size) {
>  			/*
> @@ -1590,6 +1601,12 @@ static int __split_and_process_non_flush(struct clone_info *ci)
>  	if (__process_abnormal_io(ci, ti, &r))
>  		return r;
>  
> +	/*
> +	 * Only support bio polling for normal IO, and the target io is
> +	 * exactly inside the dm io instance
> +	 */
> +	ci->io->submit_as_polled = !!(ci->bio->bi_opf & REQ_POLLED);
> +
>  	len = min_t(sector_t, max_io_len(ti, ci->sector), ci->sector_count);
>  
>  	r = __clone_and_map_data_bio(ci, ti, ci->sector, &len);
> @@ -1608,6 +1625,22 @@ static void init_clone_info(struct clone_info *ci, struct mapped_device *md,
>  	ci->map = map;
>  	ci->io = alloc_io(md, bio);
>  	ci->sector = bio->bi_iter.bi_sector;
> +
> +	if (bio->bi_opf & REQ_POLLED) {
> +		INIT_HLIST_NODE(&ci->io->node);
> +
> +		/*
> +		 * Save .bi_end_io into dm_io, so that we can reuse .bi_end_io
> +		 * for storing dm_io list
> +		 */
> +		if (bio->bi_opf & REQ_SAVED_END_IO) {
> +			ci->io->saved_bio_end_io = NULL;
> +		} else {
> +			ci->io->saved_bio_end_io = bio->bi_end_io;
> +			INIT_HLIST_HEAD((struct hlist_head *)&bio->bi_end_io);
> +			bio->bi_opf |= REQ_SAVED_END_IO;
> +		}
> +	}
>  }
>  
>  #define __dm_part_stat_sub(part, field, subnd)	\
> @@ -1666,8 +1699,19 @@ static void __split_and_process_bio(struct mapped_device *md,
>  		}
>  	}
>  
> -	/* drop the extra reference count */
> -	dec_pending(ci.io, errno_to_blk_status(error));
> +	/*
> +	 * Drop the extra reference count for non-POLLED bio, and hold one
> +	 * reference for POLLED bio, which will be released in dm_poll_bio
> +	 *
> +	 * Add every dm_io instance into the hlist_head which is stored in
> +	 * bio->bi_end_io, so that dm_poll_bio can poll them all.
> +	 */
> +	if (!ci.io->submit_as_polled)
> +		dec_pending(ci.io, errno_to_blk_status(error));
> +	else
> +		hlist_add_head(&ci.io->node,
> +				(struct hlist_head *)&bio->bi_end_io);
> +
>  }
>  
>  static void dm_submit_bio(struct bio *bio)
> @@ -1707,6 +1751,66 @@ static void dm_submit_bio(struct bio *bio)
>  	dm_put_live_table(md, srcu_idx);
>  }
>  
> +static int dm_poll_dm_io(struct dm_io *io, unsigned int flags)
> +{
> +	if (!io || !io->submit_as_polled)
> +		return 0;

Wondering if '!io->submit_as_polled' is necessary here. dm_io will be
added into the hash list only when 'io->submit_as_polled' is true in
__split_and_process_bio.


> +
> +	WARN_ON_ONCE(!io->tio.inside_dm_io);
> +	bio_poll(&io->tio.clone, flags);
> +
> +	/* bio_poll holds the last reference */
> +	if (atomic_read(&io->io_count) == 1)
> +		return 1;
> +	return 0;
> +}
> +
> +static int dm_poll_bio(struct bio *bio, unsigned int flags)
> +{
> +	struct dm_io *io;
> +	void *saved_bi_end_io = NULL;
> +	struct hlist_head tmp = HLIST_HEAD_INIT;
> +	struct hlist_head *head = (struct hlist_head *)&bio->bi_end_io;
> +	struct hlist_node *next;
> +
> +	/*
> +	 * This bio can be submitted from FS as POLLED so that FS may keep
> +	 * polling even though the flag is cleared by bio splitting or
> +	 * requeue, so return immediately.
> +	 */
> +	if (!(bio->bi_opf & REQ_POLLED))
> +		return 0;
> +
> +	hlist_move_list(head, &tmp);
> +
> +	hlist_for_each_entry(io, &tmp, node) {
> +		if (io->saved_bio_end_io && !saved_bi_end_io) {

Seems that checking if saved_bi_end_io NULL here is not necessary, since
you will exit thte loop once saved_bi_end_io is assigned.



> +			saved_bi_end_io = io->saved_bio_end_io;
> +			break;
> +		}
> +	}
> +
> +	/* restore .bi_end_io before completing dm io */
> +	WARN_ON_ONCE(!saved_bi_end_io);

Abnormal bio flagged with REQ_POLLED (is this possible?) can still be
called with dm_poll_bio(), and will trigger this warning.


> +	bio->bi_end_io = saved_bi_end_io;
> +
> +	hlist_for_each_entry_safe(io, next, &tmp, node) {
> +		if (dm_poll_dm_io(io, flags)) {
> +			hlist_del_init(&io->node);
> +			dec_pending(io, 0);
> +		}
> +	}
> +
> +	/* Not done, make sure at least one dm_io stores the .bi_end_io*/
> +	if (!hlist_empty(&tmp)) {
> +		io = hlist_entry(tmp.first, struct dm_io, node);
> +		io->saved_bio_end_io = saved_bi_end_io;
> +		hlist_move_list(&tmp, head);
> +		return 0;> +	}
> +	return 1;
> +}
> +
>  /*-----------------------------------------------------------------
>   * An IDR is used to keep track of allocated minor numbers.
>   *---------------------------------------------------------------*/
> @@ -3121,6 +3225,7 @@ static const struct pr_ops dm_pr_ops = {
>  
>  static const struct block_device_operations dm_blk_dops = {
>  	.submit_bio = dm_submit_bio,
> +	.poll_bio = dm_poll_bio,
>  	.open = dm_blk_open,
>  	.release = dm_blk_close,
>  	.ioctl = dm_blk_ioctl,
> 

-- 
Thanks,
Jeffle

--
dm-devel mailing list
dm-devel@redhat.com
https://listman.redhat.com/mailman/listinfo/dm-devel


  parent reply	other threads:[~2021-06-28  9:52 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-06-17 10:35 [dm-devel] [RFC PATCH V2 0/3] block/dm: support bio polling Ming Lei
2021-06-17 10:35 ` [dm-devel] [RFC PATCH V2 1/3] block: add helper of blk_queue_poll Ming Lei
2021-06-21  7:20   ` Christoph Hellwig
2021-06-21  8:38     ` Ming Lei
2021-06-17 10:35 ` [dm-devel] [RFC PATCH V2 2/3] block: add ->poll_bio to block_device_operations Ming Lei
2021-06-21  7:25   ` Christoph Hellwig
2021-06-21  8:41     ` Ming Lei
2021-06-17 10:35 ` [dm-devel] [RFC PATCH V2 3/3] dm: support bio polling Ming Lei
2021-06-17 23:08   ` Ming Lei
2021-06-18  8:19   ` JeffleXu [this message]
2021-06-18 13:29     ` Ming Lei
2021-06-18 14:39     ` Ming Lei
2021-06-18 20:56       ` Mike Snitzer
2021-06-19  0:27         ` Ming Lei
2021-06-21  1:32         ` JeffleXu
2021-06-21 11:33       ` JeffleXu
2021-06-21 14:04         ` Ming Lei
2021-06-22  2:26           ` JeffleXu
2021-06-22  2:45             ` Ming Lei
2021-06-22  7:45               ` JeffleXu
2021-06-30  8:30         ` Ming Lei
2021-06-21  7:36   ` Christoph Hellwig
2021-06-21  9:09     ` Ming Lei

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=5ba43dac-b960-7c85-3a89-fdae2d1e2f51@linux.alibaba.com \
    --to=jefflexu@linux.alibaba.com \
    --cc=axboe@kernel.dk \
    --cc=dm-devel@redhat.com \
    --cc=hch@lst.de \
    --cc=linux-block@vger.kernel.org \
    --cc=ming.lei@redhat.com \
    --cc=snitzer@redhat.com \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).