linux-kernel - Re: [PATCH 2/2] block: make /sys/block/<dev>/queue/discard_max

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Message-ID: <20150714152332.GA5568@redhat.com>
Date:	Tue, 14 Jul 2015 11:23:32 -0400
From:	Mike Snitzer <snitzer@...hat.com>
To:	Jens Axboe <axboe@...com>
Cc:	linux-kernel@...r.kernel.org, hch@....de
Subject: Re: [PATCH 2/2] block: make /sys/block/<dev>/queue/discard_max_bytes
 writeable

On Tue, Jul 14 2015 at 11:02am -0400,
Jens Axboe <axboe@...com> wrote:

> Lots of devices support huge discard sizes these days. Depending
> on how the device handles them internally, huge discards can
> introduce massive latencies (hundreds of msec) on the device side.
> 
> We have a sysfs file, discard_max_bytes, that advertises the max
> hardware supported discard size. Make this writeable, and split
> the settings into a soft and hard limit. This can be set from
> 'discard_granularity' and up to the hardware limit.

Looks pretty good, but we'll lose the original discard_max_bytes once it
is changed.  That information loss will prevent users from knowing what
adjustments are possible over time.

This may be OK, but figured i'd raise it.
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