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

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Date:	Tue, 03 Jul 2012 16:21:34 +0200
From:	Paolo Bonzini <pbonzini@...hat.com>
To:	Vivek Goyal <vgoyal@...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

Il 03/07/2012 16:00, Vivek Goyal ha scritto:
>> > 
>> > Ah, interesting, I missed it completely.  I guess it's because queue/
>> > directories only exist for full disks, and the correct alignment varies
>> > for each partition.  So this patch is unnecessary.
> Partition discard_alignments are available in
> /sys/block/<disk>/<partition>/discard_alignment.

Yes.  If it were in queue/, it wouldn't be available.

> 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?

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;
 
 	/*
 	 * Ensure that max_discard_sectors is of the proper

Paolo
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