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From: Evan Green <evgreen@chromium.org>
To: martin.petersen@oracle.com
Cc: ming.lei@redhat.com, axboe@kernel.dk,
	Gwendal Grignou <gwendal@chromium.org>,
	asavery@chromium.org, linux-block@vger.kernel.org,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/2] loop: Better discard support for block devices
Date: Mon, 10 Dec 2018 09:31:27 -0800	[thread overview]
Message-ID: <CAE=gft7ymeVu0chvCYWn8tw9ss_pZgyUHt=5sSdxfRenDD46Xw@mail.gmail.com> (raw)
In-Reply-To: <yq1va47pcqp.fsf@oracle.com>

On Wed, Dec 5, 2018 at 7:15 PM Martin K. Petersen
<martin.petersen@oracle.com> wrote:
>
>
> Evan,
>
> > Ah, I see. But I think it's useful to reflect max_discard_sectors,
> > max_write_zeroes_sectors, discard_granularity, and discard_alignment
> > from the block device to the loop device. With the exception of
> > discard_alignment, these parameters are visible via sysfs,
>
> discard_alignment is visible in sysfs, just not in the queue directory
> since alignment can be different on a per-partition basis. So there is
> one discard_alignment at the root of each /sys/block/foo directory and
> one for each partition subdirectory. This mirrors the alignment_offset
> variable which indicates a partitions alignment wrt. the underlying
> physical block size.
>
> That said, there are not many devices that actually report a non-zero
> discard alignment so it's not as useful as the device manufacturers
> (that were looking for an implementation shortcut) envisioned.

Ah ok, thanks.

>
> > I'm not totally sure about discard_alignment, that seems to be useful
> > in cases of merging blk requests. So I can stop mirroring that one if
> > it's harmful or not helpful. But unless it's a nak, I'd really love to
> > keep most of the mirroring. In which case the bool doesn't do a whole
> > lot of simplifying.
>
> I think it's fine to export these. The block device topology was
> explicitly designed to be stackable like this.

Yeah, it seemed to fall in pretty naturally, which is why I was hoping
it might not be so controversial. Thanks Martin.
-Evan

  reply	other threads:[~2018-12-10 17:32 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-10-30 23:06 [PATCH 0/2] loop: Better discard " Evan Green
2018-10-30 23:06 ` [PATCH 1/2] loop: Report EOPNOTSUPP properly Evan Green
2018-11-28  1:06   ` Ming Lei
2018-10-30 23:06 ` [PATCH 2/2] loop: Better discard support for block devices Evan Green
2018-11-26 18:53   ` Evan Green
2018-11-27  2:55     ` Ming Lei
2018-11-27 23:34       ` Evan Green
2018-11-28  1:28         ` Ming Lei
2018-11-28  1:26   ` Ming Lei
2018-12-04 22:19     ` Evan Green
2018-12-05  1:10       ` Ming Lei
2018-12-05 19:35         ` Evan Green
2018-12-06  0:22           ` Ming Lei
2018-12-06  3:15           ` Martin K. Petersen
2018-12-10 17:31             ` Evan Green [this message]
2018-12-18 23:48               ` Evan Green
2018-10-30 23:50 ` [PATCH 0/2] loop: Better discard " Bart Van Assche
2018-11-01 18:15   ` Evan Green
2018-11-01 22:44     ` Gwendal Grignou
2018-11-02 16:02       ` Bart Van Assche
2018-11-05 20:35         ` Evan Green

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