From: Theodore Tso Subject: Re: [PATCH] Improve buffered streaming write ordering Date: Tue, 7 Oct 2008 09:29:11 -0400 Message-ID: <20081007132911.GA6905@mit.edu> References: <20081001215239.ee2ae63f.akpm@linux-foundation.org> <1222950054.6745.18.camel@think.oraclecorp.com> <20081002181856.GB29613@skywalker> <20081002234309.GH30001@disturbed> <1223063155.13375.64.camel@think.oraclecorp.com> <20081006101605.GA15881@skywalker> <1223302903.16546.58.camel@think.oraclecorp.com> <20081007084531.GB15881@skywalker> <20081007090554.GA23811@infradead.org> <20081007100257.GA30745@skywalker> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Christoph Hellwig , Chris Mason , Dave Chinner , Andrew Morton , linux-kernel , linux-fsdevel , ext4 To: "Aneesh Kumar K.V" Return-path: Received: from www.church-of-our-saviour.org ([69.25.196.31]:46111 "EHLO thunker.thunk.org" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1753384AbYJGNab (ORCPT ); Tue, 7 Oct 2008 09:30:31 -0400 Content-Disposition: inline In-Reply-To: <20081007100257.GA30745@skywalker> Sender: linux-ext4-owner@vger.kernel.org List-ID: On Tue, Oct 07, 2008 at 03:32:57PM +0530, Aneesh Kumar K.V wrote: > On Tue, Oct 07, 2008 at 05:05:54AM -0400, Christoph Hellwig wrote: > > On Tue, Oct 07, 2008 at 02:15:31PM +0530, Aneesh Kumar K.V wrote: > > > +static int ext4_write_cache_pages(struct address_space *mapping, > > > + struct writeback_control *wbc, writepage_t writepage, > > > + void *data) > > > +{ > > > > Looking at this functions the only difference is killing the > > writeback_index and range_start updates. If they are bad why would we > > only remove them from ext4? > > I am also not updating wbc->nr_to_write. ... > I don't think other filesystem have this requirement. That's true, but there is a lot of code duplication, which means that bugs or changes in write_cache_pages() would need to be fixed in ext4_write_cache_pages(). So another approach that might be better from a long-term code maintenance point of view is to add a flag in struct writeback_control that tells write_cache_pages() not to update those fields, and avoid duplicating approximately 95 lines of code. It means a change in a core mm function, though, so if folks thinks its too ugly, we can make our own copy in fs/ext4. Opinions? Andrew, as someone who often weighs in on fs and mm issues, what do you think? My preference would be to make the change to mm/page-writeback.c, controlled by a flag which ext4 would set be set by fs/ext4 before it calls write_cache_pages(). - Ted