From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758298Ab1CCOIH (ORCPT ); Thu, 3 Mar 2011 09:08:07 -0500 Received: from cantor2.suse.de ([195.135.220.15]:54643 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755657Ab1CCOIF (ORCPT ); Thu, 3 Mar 2011 09:08:05 -0500 Date: Thu, 3 Mar 2011 15:08:02 +0100 From: Jan Kara To: Wu Fengguang Cc: "Jun'ichi Nomura" , Jan Kara , "linux-kernel@vger.kernel.org" , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH] Fix mapping->writeback_index to point to the last written page Message-ID: <20110303140802.GA27751@quack.suse.cz> References: <4D676067.8050200@ce.jp.nec.com> <20110302221808.GG7496@quack.suse.cz> <4D6EFC4B.30505@ce.jp.nec.com> <20110303133119.GA16562@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110303133119.GA16562@localhost> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu 03-03-11 21:31:19, Wu Fengguang wrote: > On Thu, Mar 03, 2011 at 10:26:19AM +0800, Jun'ichi Nomura wrote: > > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899962 + 8 > > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899970 + 8 > > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899978 + 8 > > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899986 + 8 > > flush-8:0-2743 4606: block_bio_queue: 8,0 W 94899994 + 8 > ==> > kworker/0:1-11 4606: block_rq_issue: 8,0 W 0 () 94899962 + 40 > > >> flush-8:0-2743 4606: block_bio_queue: 8,0 W 94898554 + 8 > ==> > >> flush-8:0-2743 4606: block_rq_issue: 8,0 W 0 () 94898554 + 8 > > I'd expect the wrapped around 94898554+8 to be merged with 94899962+8. How could they be merged? They are not continguous... > Why kworker/0:1-11 is submitting the request early? And the second > request is submitted by flush-8:0-2743. I'm not sure about that either - but I think that kworker is submitting the work when unplug happens while flush ends up doing it when the queue is alredy unplugged. > > The 1st writeback ended at block 94898562. (94898554+8) > > The 2nd writeback started there. > > However, since the last page at the 1st writeback was just redirtied, > > the 2nd writeback looped back to block 94898554 after sequentially > > submitting blocks from 94898562 to 94900001. > > > > 1 extra seek which could be avoided. > > I haven't seen fatal problem with the latest kernel, though. > > > > With older kernels (before 2.6.29, without commit 31a12666), > > kupdate leaves the dirty pages like spots until the application wraps > > around the ring. (It could take hours to days.) > > That led me to this code. > > > > > But as I'm thinking about it, it wouldn't harm our original aim to do > > > what you propose and it can help this relatively common case. So I think > > > it's a good idea. Fengguang, what do you think? > > I see no problem too. > > Tested-by: Wu Fengguang OK, I'll update the changelog to reflect our discussion and post the patch to Andrew for inclusion. Honza