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

To: Vivek Goyal <vgoyal@xxxxxxxxxx>
Subject: Re: [dm-devel] [PATCH v2 1/3] block: add sysfs entry for discard_alignment
From: Paolo Bonzini <pbonzini@xxxxxxxxxx>
Date: Tue, 03 Jul 2012 16:21:34 +0200
Cc: linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, snitzer@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, david@xxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, hch@xxxxxx
In-reply-to: <20120703140048.GC11272@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>
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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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