From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Chinner Subject: Re: [PATCH 3/3] blkdev: honor discard_granularity in blkdev_issue_discard() Date: Tue, 3 May 2011 09:21:21 +1000 Message-ID: <20110502232121.GD2978@dastard> References: <1304345841-20063-1-git-send-email-lczerner@redhat.com> <1304345841-20063-3-git-send-email-lczerner@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Lukas Czerner , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Dmitry Monakhov , Jens Axboe To: "Martin K. Petersen" Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Mon, May 02, 2011 at 10:38:38AM -0400, Martin K. Petersen wrote: > >>>>> "Lukas" == Lukas Czerner writes: > > Lukas> As Jeff Moyer pointed out we do not honor discard granularity > Lukas> while submitting REQ_DISCARD bios of size smaller than > Lukas> max_discard_sectors. That fact might have unwanted consequences > Lukas> of device ignoring the request, or even worse if device firmware > Lukas> is buggy. > > We've discussed this before and the consensus was not to do it. The > granularity is a hint, not a hard limit like max_discard_sectors. > > We want the reporting to be comprehensive throughout the block layer. If > we start aligning to the granularity at the top we lose information for > stacked devices below with a finer granularity. > > So if we were to align to the granularity we'd want to do it at the > bottom of the stack when we issue the command to the device. We've had a > few proposed patches to did that but so far we've only found one device > where it made a difference. And that case didn't justify adding a quirk. Adding this comment to the code to explain why we don't enforce the granularity would be a good idea, yes? Cheers, Dave. -- Dave Chinner david@fromorbit.com