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From: "Martin K. Petersen" <martin.petersen@oracle.com>
To: Evan Green <evgreen@chromium.org>
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: Wed, 05 Dec 2018 22:15:10 -0500	[thread overview]
Message-ID: <yq1va47pcqp.fsf@oracle.com> (raw)
In-Reply-To: <CAE=gft7K2OrN93c8TQ5ozOpXzXf5ZD-PNnVHWP9SbZXZqp2dHw@mail.gmail.com> (Evan Green's message of "Wed, 5 Dec 2018 11:35:57 -0800")


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.

> 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.

-- 
Martin K. Petersen	Oracle Linux Engineering

  parent reply	other threads:[~2018-12-06  3:15 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 [this message]
2018-12-10 17:31             ` Evan Green
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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