From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: dm-thin: Export proper discard_granularity Date: Wed, 11 Jun 2014 17:31:35 -0400 Message-ID: <20140611213134.GA22986@redhat.com> References: <1402489929-16466-1-git-send-email-lczerner@redhat.com> Reply-To: device-mapper development Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: Content-Disposition: inline In-Reply-To: <1402489929-16466-1-git-send-email-lczerner@redhat.com> List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: dm-devel-bounces@redhat.com Errors-To: dm-devel-bounces@redhat.com To: Lukas Czerner Cc: dm-devel@redhat.com List-Id: dm-devel.ids On Wed, Jun 11 2014 at 8:32am -0400, Lukas Czerner wrote: > Currently if the underlying device is discard capable and the > discard_passdown is enabled, the discard_granularity will be inherited > from that device. > > This will pose a problem in the case that the device discard_granularity > is smaller than thin volume chunk size, because in that case discard > requests will not be chunk size aligned so it will be ignored by > dm-thin. > > Fix this by setting thin volume discard granularity to the bigger of the > two max(device discard_granularity, thin volume chunk size). Strictly > speaking it is not necessary to get the bigger of the two, because > the thin volume chunk size will always be >= device discard_granularity. > However I believe that the reason for this is only because dm-thin can > not handle discard requests bigger than chunk size which is hopefully > going to change soon. This way it is future proof. > > RHBZ: 1106856 > > Reported-by: Zdenek Kabelac > Signed-off-by: Lukas Czerner Hi Lukas, I missed this submission on dm-devel until now. But I had already picked this patch up earlier from the BZ, see the patch I staged in linux-next here: https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=09869de57ed2728ae3c619803932a86cb0e2c4f8