linux-kernel - Re: [PATCH 42/41 v2] dm: convey that all flushes are processed as empty

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Message-ID: <4C87B51C.6050703@kernel.org>
Date:	Wed, 08 Sep 2010 18:09:00 +0200
From:	Tejun Heo <tj@...nel.org>
To:	Mike Snitzer <snitzer@...hat.com>
CC:	Christoph Hellwig <hch@....de>, jack@...e.cz, mst@...hat.com,
	linux-ide@...r.kernel.org,
	device-mapper development <dm-devel@...hat.com>,
	James.Bottomley@...e.de, konishi.ryusuke@....ntt.co.jp,
	k-ueda@...jp.nec.com, vst@...b.net, linux-scsi@...r.kernel.org,
	rusty@...tcorp.com.au, linux-raid@...r.kernel.org,
	mpatocka@...hat.com, swhiteho@...hat.com, chris.mason@...cle.com,
	tytso@....edu, jaxboe@...ionio.com, linux-kernel@...r.kernel.org,
	linux-fsdevel@...r.kernel.org, rwheeler@...hat.com,
	Milan Broz <mbroz@...hat.com>
Subject: Re: [PATCH 42/41 v2] dm: convey that all flushes are processed as
 empty

On 09/08/2010 04:04 AM, Mike Snitzer wrote:
> Rename __clone_and_map_flush to __clone_and_map_empty_flush for added
> clarity.
> 
> Simplify logic associated with REQ_FLUSH conditionals.
> 
> Introduce a BUG_ON() and add a few more helpful comments to the code
> so that it is clear that all flushes are empty.
> 
> Cleanup __split_and_process_bio() so that an empty flush isn't processed
> by a 'sector_count' focused while loop.
> 
> Signed-off-by: Mike Snitzer <snitzer@...hat.com>
> ---
>  drivers/md/dm.c |   34 +++++++++++++++-------------------
>  1 files changed, 15 insertions(+), 19 deletions(-)
> 
> Tejun, please feel free to fold this patch into (or insert after)
> 0025-dm-relax-ordering-of-bio-based-flush-implementation.patch
> 
> v2: Simplify logic associated with REQ_FLUSH conditionals
> 
> diff --git a/drivers/md/dm.c b/drivers/md/dm.c
> index cd2f7e7..f934e98 100644
> --- a/drivers/md/dm.c
> +++ b/drivers/md/dm.c
> @@ -621,16 +621,17 @@ static void dec_pending(struct dm_io *io, int error)
>  		if (io_error == DM_ENDIO_REQUEUE)
>  			return;
>  
> -		if (!(bio->bi_rw & REQ_FLUSH) || !bio->bi_size) {
> -			trace_block_bio_complete(md->queue, bio);
> -			bio_endio(bio, io_error);
> -		} else {
> +		if ((bio->bi_rw & REQ_FLUSH) && bio->bi_size) {
>  			/*
>  			 * Preflush done for flush with data, reissue
>  			 * without REQ_FLUSH.
>  			 */
>  			bio->bi_rw &= ~REQ_FLUSH;
>  			queue_io(md, bio);
> +		} else {
> +			/* done with normal IO or empty flush */
> +			trace_block_bio_complete(md->queue, bio);
> +			bio_endio(bio, io_error);
>  		}
>  	}
>  }
> @@ -1132,16 +1133,15 @@ static void __issue_target_requests(struct clone_info *ci, struct dm_target *ti,
>  		__issue_target_request(ci, ti, request_nr, len);
>  }
>  
> -static int __clone_and_map_flush(struct clone_info *ci)
> +static int __clone_and_map_empty_flush(struct clone_info *ci)
>  {
>  	unsigned target_nr = 0;
>  	struct dm_target *ti;
>  
> +	BUG_ON(bio_has_data(ci->bio));
>  	while ((ti = dm_table_get_target(ci->map, target_nr++)))
>  		__issue_target_requests(ci, ti, ti->num_flush_requests, 0);
>  
> -	ci->sector_count = 0;
> -
>  	return 0;
>  }
>  
> @@ -1282,7 +1282,6 @@ static int __clone_and_map(struct clone_info *ci)
>   */
>  static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
>  {
> -	bool is_flush = bio->bi_rw & REQ_FLUSH;
>  	struct clone_info ci;
>  	int error = 0;
>  
> @@ -1302,20 +1301,17 @@ static void __split_and_process_bio(struct mapped_device *md, struct bio *bio)
>  	ci.sector = bio->bi_sector;
>  	ci.idx = bio->bi_idx;
>  
> -	if (!is_flush) {
> +	start_io_acct(ci.io);
> +	if (bio->bi_rw & REQ_FLUSH) {
> +		ci.bio = &ci.md->flush_bio;
> +		ci.sector_count = 0;
> +		error = __clone_and_map_empty_flush(&ci);
> +		/* dec_pending submits any data associated with flush */
> +	} else {
>  		ci.bio = bio;
>  		ci.sector_count = bio_sectors(bio);
> -	} else {
> -		ci.bio = &ci.md->flush_bio;
> -		ci.sector_count = 1;
> -	}
> -
> -	start_io_acct(ci.io);
> -	while (ci.sector_count && !error) {
> -		if (!is_flush)
> +		while (ci.sector_count && !error)
>  			error = __clone_and_map(&ci);
> -		else
> -			error = __clone_and_map_flush(&ci);
>  	}
>  
>  	/* drop the extra reference count */


-- 
tejun
--
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