From: Theodore Ts'o Subject: Re: jbd2: don't wake kjournald unnecessarily Date: Wed, 30 Jan 2013 00:26:58 -0500 Message-ID: <20130130052658.GE25006@thunk.org> References: <20130121140738.GI5588@quack.suse.cz> <20130121231130.GB12410@thunk.org> <20130122235041.GA7497@quack.suse.cz> <50FF3EEA.2030408@redhat.com> <20130123094421.GB9821@quack.suse.cz> <50FFFFC6.8070308@redhat.com> <20130123192911.GB21112@quack.suse.cz> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Eric Sandeen , Sedat Dilek , Ext4 Developers List , mszeredi@suse.cz To: Jan Kara Return-path: Received: from li9-11.members.linode.com ([67.18.176.11]:46143 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750732Ab3A3F1F (ORCPT ); Wed, 30 Jan 2013 00:27:05 -0500 Content-Disposition: inline In-Reply-To: <20130123192911.GB21112@quack.suse.cz> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Wed, Jan 23, 2013 at 08:29:11PM +0100, Jan Kara wrote: > > old JBD: AIM7 jobs/min 97624.39; got 78193 jbd wakeups > > new JBD: AIM7 jobs/min 85929.43; got 6306999 jbd wakeups, 6264684 extra wakeups > Yeah, that's a lot. My guess would be *a lot* of processes are hanging in > start_this_handle() and waiting for transaction commit. Each of them calls > __log_start_commit() and things add up. Thanks for getting these numbers. Yeah, wow. That would imply that there are a huge number of processes that get hung up in start_this_handle(), and they are waking up the journal before the kjournald has a chance to set T_LOCKED (since then they would get blocked earlier in start_this_handle). Given that, I wonder if the following change would actually help or hurt things. Eric, would you be willing to ask your perf team to try testing out these patches? - Ted