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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 10:00:48 -0400
Cc: linux-kernel@xxxxxxxxxxxxxxx, axboe@xxxxxxxxx, snitzer@xxxxxxxxxx, martin.petersen@xxxxxxxxxx, david@xxxxxxxxxxxxx, xfs@xxxxxxxxxxx, dm-devel@xxxxxxxxxx, hch@xxxxxx
In-reply-to: <4FF2DCB1.2090704@xxxxxxxxxx>
References: <1341235225-27551-1-git-send-email-pbonzini@xxxxxxxxxx> <1341235225-27551-2-git-send-email-pbonzini@xxxxxxxxxx> <20120703023442.GB3586@xxxxxxxxxx> <4FF2DCB1.2090704@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Tue, Jul 03, 2012 at 01:51:13PM +0200, Paolo Bonzini wrote:
> Il 03/07/2012 04:34, Vivek Goyal ha scritto:
> >> > The next patches will actually use the alignment, expose it in sysfs
> >> > for ease of debugging.
> >> > 
> > Don't we already have discard_alignment exported as device attribute.
> > 
> > /sys/block/<dev>/discard_alignment
> 
> 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.

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?

Thanks
Vivek

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