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

To: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Subject: Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for discard_alignment
From: Vivek Goyal <vgoyal@xxxxxxxxxx>
Date: Tue, 3 Jul 2012 10:39:49 -0400
Cc: linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, snitzer@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, david@xxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, hch@xxxxxx
In-reply-to: <4FF2FFEE.4000401@xxxxxxxxxx>
References: <1341235225-27551-1-git-send-email-pbonzini@xxxxxxxxxx> <1341235225-27551-2-git-send-email-pbonzini@xxxxxxxxxx> <20120703023442.GB3586@xxxxxxxxxx> <4FF2DCB1.2090704@xxxxxxxxxx> <20120703140048.GC11272@xxxxxxxxxx> <4FF2FFEE.4000401@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
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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