From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754067Ab1DVCcq (ORCPT ); Thu, 21 Apr 2011 22:32:46 -0400 Received: from mga09.intel.com ([134.134.136.24]:53003 "EHLO mga09.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753202Ab1DVCco (ORCPT ); Thu, 21 Apr 2011 22:32:44 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.64,252,1301900400"; d="scan'208";a="632408773" Date: Fri, 22 Apr 2011 10:32:26 +0800 From: Wu Fengguang To: Jan Kara Cc: Christoph Hellwig , Andrew Morton , Mel Gorman , Dave Chinner , Trond Myklebust , Itaru Kitayama , Minchan Kim , LKML , "linux-fsdevel@vger.kernel.org" , Linux Memory Management List Subject: Re: [PATCH 5/6] writeback: try more writeback as long as something was written Message-ID: <20110422023226.GB6199@localhost> References: <20110419030532.778889102@intel.com> <20110419102016.GD5257@quack.suse.cz> <20110419111601.GA18961@localhost> <20110419211008.GD9556@quack.suse.cz> <20110420075053.GB30672@localhost> <20110420152211.GC4991@quack.suse.cz> <20110421033325.GA13764@localhost> <20110421043940.GC22423@infradead.org> <20110421060556.GA24232@localhost> <20110421164154.GC4476@quack.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110421164154.GC4476@quack.suse.cz> 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 Fri, Apr 22, 2011 at 12:41:54AM +0800, Jan Kara wrote: > On Thu 21-04-11 14:05:56, Wu Fengguang wrote: > > On Thu, Apr 21, 2011 at 12:39:40PM +0800, Christoph Hellwig wrote: > > > On Thu, Apr 21, 2011 at 11:33:25AM +0800, Wu Fengguang wrote: > > > > I collected the writeback_single_inode() traces (patch attached for > > > > your reference) each for several test runs, and find much more > > > > I_DIRTY_PAGES after patchset. Dave, do you know why there are so many > > > > I_DIRTY_PAGES (or radix tag) remained after the XFS ->writepages() call, > > > > even for small files? > > > > > > What is your defintion of a small file? As soon as it has multiple > > > extents or holes there's absolutely no way to clean it with a single > > > writepage call. > > > > It's writing a kernel source tree to XFS. You can find in the below > > trace that it often leaves more dirty pages behind (indicated by the > > I_DIRTY_PAGES flag) after writing as less as 1 page (indicated by the > > wrote=1 field). > As Dave said, it's probably just a race since XFS redirties the inode on > IO completion. So I think the inodes are just small so they have only a few > dirty pages so you don't have much to write and they are written and > redirtied before you check the I_DIRTY flags. You could use radix tree > dirty tag to verify whether there are really dirty pages or not... Yeah, Dave and Christoph root caused it in the other email -- XFS sets I_DIRTY which accidentally sets I_DIRTY_PAGES. We can safely bet there are no real dirty pages -- otherwise it would have turned up as performance regressions. > BTW a quick check of kernel tree shows the following distribution of > sizes (in KB): > Count KB Cumulative Percent > 257 0 0.9% > 13309 4 45% > 5553 8 63% > 2997 12 73% > 1879 16 80% > 1275 20 83% > 987 24 87% > 685 28 89% > 540 32 91% > 387 36 ... > 309 40 > 264 44 > 249 48 > 170 52 > 143 56 > 144 60 > 132 64 > 100 68 > ... > Total 30155 > > And the distribution of your 'wrote=xxx' roughly corresponds to this... Nice numbers! How do you manage to account them? :) Thanks, Fengguang