From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH for-4.2 2/3] block, dm: don't copy bios for request clones Date: Fri, 29 May 2015 18:54:51 +0200 Message-ID: <20150529165451.GA2682@lst.de> References: <1432300445-9543-1-git-send-email-snitzer@redhat.com> <1432300445-9543-2-git-send-email-snitzer@redhat.com> <556410BB.3000103@ce.jp.nec.com> <20150527082157.GA25993@lst.de> <5565935A.4060408@ce.jp.nec.com> <5566B7E5.1070101@ce.jp.nec.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: <5566B7E5.1070101@ce.jp.nec.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: Junichi Nomura Cc: Jens Axboe , device-mapper development , Christoph Hellwig , Mike Snitzer List-Id: dm-devel.ids On Thu, May 28, 2015 at 06:38:29AM +0000, Junichi Nomura wrote: > I'm also worried about partial completion case. > For successful partial completion, current code completes > bio before fully completing the request. > Your patch changes bios not completed until the request is > fully completed. Yes. Why are you worried about this case? > I'm not very sure how much impact does the removal of partial > completion have in the real world. > If partial completion is so negligible, I think it should be > handled in such a way all the cases, instead of special casing > REQ_CLONE. It isn't negligible - under load it actually does matter that we handle partial completions as arrays decide to just complete a request partially, so if we don't handle them we might end up in a loop not making progress. But if we only do that once on path fail over it's not an actual issue.