From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jens Axboe Subject: Re: block: fix alignment_offset math that assumes io_min is a power-of-2 Date: Wed, 08 Oct 2014 16:38:13 -0600 Message-ID: <5435BCD5.9050306@kernel.dk> References: <1412805952-15316-1-git-send-email-snitzer@redhat.com> <5435B6C0.8020704@kernel.dk> <20141008222841.GA15345@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20141008222841.GA15345@redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Mike Snitzer Cc: linux-kernel@vger.kernel.org, dm-devel@redhat.com, martin.petersen@oracle.com List-Id: dm-devel.ids On 10/08/2014 04:28 PM, Mike Snitzer wrote: > On Wed, Oct 08 2014 at 6:12pm -0400, > Jens Axboe wrote: > >> 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... > > Yeah, certainly does suck (please note v2 that I just sent). The MODs > shouldn't kill us, these functions aren't called in any real hot path. > A storm at boot maybe.. or SCSI rescan but... I had it mixed up with the recent blk_max_size_offset() - you are right, this is not in a hot path. For that case, I don't really care, it's fine. Is v2 runtime tested? -- Jens Axboe