From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail137.messagelabs.com (mail137.messagelabs.com [216.82.249.19]) by kanga.kvack.org (Postfix) with SMTP id D30A36B00C0 for ; Wed, 29 Jul 2009 21:49:14 -0400 (EDT) Date: Thu, 30 Jul 2009 09:49:17 +0800 From: Wu Fengguang Subject: Re: Bug in kernel 2.6.31, Slow wb_kupdate writeout Message-ID: <20090730014917.GB7326@localhost> References: <1786ab030907281211x6e432ba6ha6afe9de73f24e0c@mail.gmail.com> <33307c790907281449k5e8d4f6cib2c93848f5ec2661@mail.gmail.com> <33307c790907290015m1e6b5666x9c0014cdaf5ed08@mail.gmail.com> <20090729114322.GA9335@localhost> <33307c790907291719r2caf7914xb543877464ba6fc2@mail.gmail.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <33307c790907291719r2caf7914xb543877464ba6fc2@mail.gmail.com> Sender: owner-linux-mm@kvack.org To: Martin Bligh Cc: Chad Talbott , "linux-kernel@vger.kernel.org" , "linux-mm@kvack.org" , Michael Rubin , Andrew Morton , "sandeen@redhat.com" , Michael Davidson List-ID: On Thu, Jul 30, 2009 at 08:19:34AM +0800, Martin Bligh wrote: > BTW, can you explain this code at the bottom of generic_sync_sb_inodes > for me? > > if (wbc->nr_to_write <= 0) { > wbc->more_io = 1; > break; > } > > I don't understand why we are setting more_io here? AFAICS, more_io > means there's more stuff to write ... I would think we'd set this if > nr_to_write was > 0 ? That's true: wbc.nr_to_write will always be set to MAX_WRITEBACK_PAGES by wb_writeback() before entering generic_sync_sb_inodes(). So wbc.nr_to_write <=0 indicates we are interrupted by the quota and should revisit generic_sync_sb_inodes() to check for more io (which will _normally_ find more dirty pages to write). > Or just have the section below brought up above this > break check and do: > > if (!list_empty(&sb->s_more_io) || !list_empty(&sb->s_io)) > wbc->more_io = 1; > > Am I just misunderstanding the intent of more_io ? It should be OK. I agree on the change if it makes the logic more straightforward. Thanks, Fengguang -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org