Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754029Ab2FMMOl (ORCPT ); Wed, 13 Jun 2012 08:14:41 -0400 Received: from mga01.intel.com ([192.55.52.88]:15188 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753986Ab2FMMOk (ORCPT ); Wed, 13 Jun 2012 08:14:40 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.71,315,1320652800"; d="scan'208";a="165096300" Date: Wed, 13 Jun 2012 20:14:34 +0800 From: Fengguang Wu To: Dave Chinner Cc: Wanpeng Li , linux-kernel@vger.kernel.org, Gavin Shan Subject: Re: [PATCH v2] writeback: avoid race when update bandwidth Message-ID: <20120613121434.GA937@localhost> References: <1339501561-4570-1-git-send-email-liwp.linux@gmail.com> <20120612115219.GA17348@localhost> <20120613035920.GV22848@dastard> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20120613035920.GV22848@dastard> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2226 Lines: 50 On Wed, Jun 13, 2012 at 01:59:20PM +1000, Dave Chinner wrote: > On Tue, Jun 12, 2012 at 07:52:19PM +0800, Fengguang Wu wrote: > > On Tue, Jun 12, 2012 at 07:46:01PM +0800, Wanpeng Li wrote: > > > From: Wanpeng Li > > > > > > "V1 -> V2" > > > * remove dirty_lock > > > > > > Since bdi->wb.list_lock is used to protect the b_* lists, > > > so the flushers who call wb_writeback to writeback pages will > > > stuck when bandwidth update policy holds this lock. In order > > > to avoid this race we can introduce a new bandwidth_lock who > > > is responsible for protecting bandwidth update policy. > > > > > > Signed-off-by: Wanpeng Li > > > > Applied with a new title "writeback: use a standalone lock for > > updating write bandwidth". "race" is sensitive because it often > > refers to some locking error. > > Fengguang - can we get some evidence that this is a contended lock > before changing the scope of it? All of the previous "breaking up > global locks" have been done based on lock contention data, so > moving back to a global lock for this needs to have the same > analysis provided... Good point. Attached is the lockstat for the case "10 disks each runs 100 dd dirtier tasks": lkp-ne02/JBOD-10HDD-thresh=4G/xfs-100dd-1-3.2.0-rc5 The wb->list_lock contention is much better than I expected, which is good. What stand out are waittime-total - &rq->lock by double_rq_lock() 6738952.13 - clockevents_lock by clockevents_notify() 2155554.37 - mapping->tree_lock by test_clear_page_writeback() 931550.13 - sb_lock by grab_super_passive() 918815.87 - &zone->lru_lock by pagevec_lru_move_fn() 912681.05 - sysfs_mutex by sysfs_permission() 24029975.20 # mutex - ip->i_lock by xfs_ilock() 18428284.10 # mrlock Thanks, Fengguang -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/