From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754222Ab1EENzN (ORCPT ); Thu, 5 May 2011 09:55:13 -0400 Received: from cantor2.suse.de ([195.135.220.15]:34621 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753911Ab1EENzL (ORCPT ); Thu, 5 May 2011 09:55:11 -0400 Date: Thu, 5 May 2011 15:55:08 +0200 From: Jan Kara To: Wu Fengguang Cc: Jan Kara , Andrew Morton , Dave Chinner , Christoph Hellwig , LKML , "linux-fsdevel@vger.kernel.org" Subject: Re: [PATCH 1/3] writeback: introduce wbc.tagged_sync for the WB_SYNC_NONE sync stage Message-ID: <20110505135508.GE5323@quack.suse.cz> References: <20110502031750.135798606@intel.com> <20110502033035.537736600@intel.com> <20110504210059.GG6968@quack.suse.cz> <20110505121402.GA1294@localhost> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20110505121402.GA1294@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 05-05-11 20:14:02, Wu Fengguang wrote: > On Thu, May 05, 2011 at 05:00:59AM +0800, Jan Kara wrote: > > On Mon 02-05-11 11:17:51, Wu Fengguang wrote: > > > sync(2) is performed in two stages: the WB_SYNC_NONE sync and the > > > WB_SYNC_ALL sync. Tag the first stage with wbc.tagged_sync and do > > > livelock prevention for it, too. > > > > > > Note that writeback_inodes_sb() is called by not only sync(), they are > > > treated the same because the other callers need also need livelock > > > prevention. > > I was thinking about this and could not find any - which other callers > > of writeback_inodes_sb() need the livelock prevention? > > For example, the writeback_inodes_sb_if_idle() call from ext4. > In general anyone that pass get_nr_dirty_pages() as work->nr_pages > may be highly over-estimating the work set. OK, I see what you mean. I agree using tagging in these cases probably makes sense. > It won't be directly livelocked since ext4 won't wait for completion, > however there is possibility the works queued behind are delayed and > livelocked. Actually it will, writeback_inodes_sb() waits for completion (because of s_umount locking). ext4 should use writeback_inodes_sb_if_idle_nr() (with some relatively small number) anyway to avoid the pauses. > Ideally simple ->nr_pages works should be given lower priority and > even may be merged with each other, and that would be future work. Merging works wanting to do the same thing would be nice. I though about it some time ago for a while but getting all the combinations right and making the merging code resonably simple was hard so I postponed it for later because it was not urgent. Honza -- Jan Kara SUSE Labs, CR