From: Tejun Heo Subject: Re: [RFC v3] ext4: Combine barrier requests coming from fsync Date: Thu, 19 Aug 2010 17:48:39 +0200 Message-ID: <4C6D5257.9040305@kernel.org> References: <4BE02C45.6010608@redhat.com> <1273002566.3755.10.camel@mingming-laptop> <20100629205102.GM15515@tux1.beaverton.ibm.com> <20100805164008.GH2901@thunk.org> <20100805164504.GI2901@thunk.org> <20100806070424.GD2109@tux1.beaverton.ibm.com> <20100809195324.GG2109@tux1.beaverton.ibm.com> <20100809210723.GA28171@infradead.org> <20100816161433.GK2109@tux1.beaverton.ibm.com> <20100819020734.GL2109@tux1.beaverton.ibm.com> <20100819085349.GA8782@infradead.org> <4C6CF6BC.3030804@kernel.org> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: "Darrick J. Wong" , "Ted Ts'o" , Mingming Cao , Ric Wheeler , linux-ext4 , linux-kernel , Keith Mannthey , Mingming Cao To: Christoph Hellwig Return-path: Received: from hera.kernel.org ([140.211.167.34]:50613 "EHLO hera.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751445Ab0HSPwj (ORCPT ); Thu, 19 Aug 2010 11:52:39 -0400 In-Reply-To: <4C6CF6BC.3030804@kernel.org> Sender: linux-ext4-owner@vger.kernel.org List-ID: Hello, again. On 08/19/2010 11:17 AM, Tejun Heo wrote: > What was the configuration? If dm was involved, both md and dm can > only process single flush request at a time. Supporing multiple > flushes in flight wouldn't be too difficult. It's just the way things > are implemented with the previous barrier implementation. It can > definitely be improved. Oh, I just realized that the current bio-based dm implementation doesn't allow other bio's to be processed if a flush is in progress. So, it's not about not being able to handle multiple flushes. The queue just stalls while flush is in progress and because it also waits for flush completion by waiting for all commands in progress to finish. It basically ends up draining and stalling everything. Shouldn't be too hard to make it better. Thanks. -- tejun