From: "Aneesh Kumar K.V" Subject: Re: [PATCH] Improve buffered streaming write ordering Date: Tue, 7 Oct 2008 15:32:57 +0530 Message-ID: <20081007100257.GA30745@skywalker> References: <1222886451.9158.34.camel@think.oraclecorp.com> <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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Chris Mason , Dave Chinner , Andrew Morton , linux-kernel , linux-fsdevel , ext4 To: Christoph Hellwig Return-path: Content-Disposition: inline In-Reply-To: <20081007090554.GA23811@infradead.org> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org 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. ext4 delayed allocation writeback is bit tricky. It does a) Look at the dirty pages and build an in memory extent of contiguous logical file blocks. If we use writecache_pages to do that it will update nr_to_write, writeback_index etc during this stage. b) Request the block allocator for 'x' blocks. We get the value x from step a. c) block allocator may return less than 'x' contiguous block. That would mean the variables updated by write_cache_pages need to corrected. The old code was doing that. Chris Mason suggested it would make it easy to use a write_cache_pages which doesn't update the variable for ext4. I don't think other filesystem have this requirement. -aneesh