linux-kernel - Re: [PATCH v2] block: fix alignment_offset math that assumes io

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Message-ID: <yq1iojudrbl.fsf@sermon.lab.mkp.net>
Date:	Wed, 08 Oct 2014 20:23:10 -0400
From:	"Martin K. Petersen" <martin.petersen@...cle.com>
To:	Mike Snitzer <snitzer@...hat.com>
Cc:	axboe@...nel.dk, linux-kernel@...r.kernel.org,
	martin.petersen@...cle.com, dm-devel@...hat.com
Subject: Re: [PATCH v2] block: fix alignment_offset math that assumes io_min is a power-of-2

>>>>> "Mike" == Mike Snitzer <snitzer@...hat.com> writes:

Mike> The math in both blk_stack_limits() and
Mike> queue_limit_alignment_offset() assume that a block device's io_min
Mike> (aka minimum_io_size) is always a power-of-2.  Fix the math such
Mike> that it works for non-power-of-2 io_min.

Mike> This issue (of alignment_offset != 0) became apparent when testing
Mike> dm-thinp with a thinp blocksize that matches a RAID6 stripesize of
Mike> 1280K.  Commit fdfb4c8c1 ("dm thin: set minimum_io_size to pool's
Mike> data block size") unlocked the potential for alignment_offset != 0
Mike> due to the dm-thin-pool's io_min possibly being a non-power-of-2.

Looks good to me, Mike.

Acked-by: Martin K. Petersen <martin.petersen@...cle.com>

-- 
Martin K. Petersen	Oracle Linux Engineering
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