From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: [PATCH] block: fix alignment_offset math that assumes io_min is a power-of-2 Date: Wed, 08 Oct 2014 16:12:16 -0600 Message-ID: <5435B6C0.8020704@kernel.dk> References: <1412805952-15316-1-git-send-email-snitzer@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <1412805952-15316-1-git-send-email-snitzer@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer , linux-kernel@vger.kernel.org Cc: martin.petersen@oracle.com, dm-devel@redhat.com List-Id: dm-devel.ids On 10/08/2014 04:05 PM, Mike Snitzer wrote: > The math in both blk_stack_limits() and queue_limit_alignment_offset() > assume that a block device's io_min (aka minimum_io_size) is always a > power-of-2. Fix the math such that it works for non-power-of-2 io_min. > > This issue (of alignment_offset != 0) became apparent when testing > dm-thinp with a thinp blocksize that matches a RAID6 stripesize of > 1280K. Commit fdfb4c8c1 ("dm thin: set minimum_io_size to pool's data > block size") unlocked the potential for alignment_offset != 0 due to > the dm-thin-pool's io_min possibly being a non-power-of-2. Well that sucks, AND with a mask is considerably cheaper than a MOD... -- Jens Axboe