linux-kernel - Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for discard

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Message-ID: <20120703143949.GE11272@redhat.com>
Date:	Tue, 3 Jul 2012 10:39:49 -0400
From:	Vivek Goyal <vgoyal@...hat.com>
To:	Paolo Bonzini <pbonzini@...hat.com>
Cc:	linux-kernel@...r.kernel.org, axboe@...nel.dk, snitzer@...hat.com,
	martin.petersen@...cle.com, david@...morbit.com, xfs@....sgi.com,
	dm-devel@...hat.com, hch@....de
Subject: Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for
 discard_alignment

On Tue, Jul 03, 2012 at 04:21:34PM +0200, Paolo Bonzini wrote:

[..]
> > That raises an interesting question for patch3. If the discard is happening to
> > a partition, shouldn't you be looking at partition discard_alignment
> > instead of always looking at queue discard_alignment?
> 
> Good point!  Like this?

This looks better.
> 
> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
> index ba43f40..3530764 100644
> --- a/include/linux/blkdev.h
> +++ b/include/linux/blkdev.h
> @@ -1125,6 +1125,16 @@ static inline int queue_limit_discard_alignment(struct queue_limits *lim, sector
>  		& (lim->discard_granularity - 1);
>  }
>  
> +static inline int bdev_discard_alignment(struct block_device *bdev)
> +{
> +	struct request_queue *q = bdev_get_queue(bdev);
> +
> +	if (bdev != bdev->bd_contains)
> +		return bdev->bd_part->discard_alignment;
> +
> +	return q->limits.discard_alignment;
> +}
> +
>  static inline unsigned int queue_discard_zeroes_data(struct request_queue *q)
>  {
>  	if (q->limits.max_discard_sectors && q->limits.discard_zeroes_data == 1)
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index b2bde5c..77d8869 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -58,7 +58,7 @@ int blkdev_issue_discard(struct block_device *bdev, sector_t sector,
>  	/* Zero-sector (unknown) and one-sector granularities are the same.  */
>  	granularity = max(q->limits.discard_granularity >> 9, 1U);
>  	mask = granularity - 1;
> -	alignment = (q->limits.discard_alignment >> 9) & mask;
> +	alignment = bdev_discard_alignment(bdev) >> 9;

Why are you removing AND with mask operation? I don't see any AND
operation being done in bdev_discard_alignment().

Thanks
Vivek
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