From mboxrd@z Thu Jan 1 00:00:00 1970 From: Vivek Goyal Subject: Re: [PATCH v3 0/2] block: improvements for discard alignment Date: Thu, 5 Jul 2012 17:43:06 -0400 Message-ID: <20120705214306.GA18063@redhat.com> References: <1341504104-1674-1-git-send-email-pbonzini@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: <1341504104-1674-1-git-send-email-pbonzini@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: Paolo Bonzini Cc: axboe@kernel.dk, martin.petersen@oracle.com, snitzer@redhat.com, david@fromorbit.com, linux-kernel@vger.kernel.org, xfs@oss.sgi.com, dm-devel@redhat.com, hch@lst.de List-Id: dm-devel.ids On Thu, Jul 05, 2012 at 06:01:42PM +0200, Paolo Bonzini wrote: > When a disk has a large discard_granularity, discards are not split with > optimal alignment; the pessimization gets bigger as discard_granularity > and max_discard_sectors become closer. > > Take the limit case of discard_granularity == max_discard_sectors == 64. > Then, if a request is submitted for 256 sectors 2..257 it will be split > like this: 2..65, 66..129, 130..193, 194..257. None of these requests > is aligned, so in fact you might end up with no discarded logical blocks > at all. With this patch, the split will be 2..63, 64..127, 128..191, > 192..255, 256..257. The patches also take the discard_alignment into > consideration. > > Patch 1 adjusts the computation of the granularity-adjusted > max_discard_sectors so that it prepares for the new code in patch 2, > which actually adjusts the split. > > v2->v3: drop addition of queue/discard_alignment to sysfs, use > correct alignment for partitions > > Paolo Bonzini (2): > block: reorganize rounding of max_discard_sectors > block: split discard into aligned requests Looks good to me. Did little testing with scsi_debug with discard_alignment=0 and discard_alignment=7 (sectors). We seem to be aligning requests better now. Acked-by: Vivek Goyal Thanks Vivek