From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mike Snitzer Subject: Re: [PATCH v3 0/2] block: improvements for discard alignment Date: Wed, 1 Aug 2012 09:40:18 -0400 Message-ID: <20120801134018.GC20830@redhat.com> References: <1341504104-1674-1-git-send-email-pbonzini@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <1341504104-1674-1-git-send-email-pbonzini@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: axboe@kernel.dk Cc: linux-kernel@vger.kernel.org, Paolo Bonzini , martin.petersen@oracle.com, david@fromorbit.com, xfs@oss.sgi.com, dm-devel@redhat.com, hch@lst.de, vgoyal@redhat.com List-Id: dm-devel.ids On Thu, Jul 05 2012 at 12:01pm -0400, 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 > > block/blk-lib.c | 41 ++++++++++++++++++++++++++++------------- > include/linux/blkdev.h | 10 ++++++++++ > 2 files changed, 38 insertions(+), 13 deletions(-) Hey Jens, Would be great to get these discard fixes in. I know both Christoph and Vivek have reviewed these changes but that isn't reflected in the patch headers. These patches eliminate misaligned discard from being sent to the dm-thinp target. Tested-by: Mike Snitzer