From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Morton Subject: Re: [RFC PATCH] ext3 writepage() journal avoidance Date: Thu, 9 Mar 2006 15:22:54 -0800 Message-ID: <20060309152254.743f4b52.akpm@osdl.org> References: <1141929562.21442.4.camel@dyn9047017100.beaverton.ibm.com> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Cc: sct@redhat.com, jack@suse.cz, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, Ext2-devel@lists.sourceforge.net Return-path: Received: from smtp.osdl.org ([65.172.181.4]:27575 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S932112AbWCIXUx (ORCPT ); Thu, 9 Mar 2006 18:20:53 -0500 To: Badari Pulavarty In-Reply-To: <1141929562.21442.4.camel@dyn9047017100.beaverton.ibm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org Badari Pulavarty wrote: > > I am trying to speed up ext3 writepage() by avoiding > journaling in non-block allocation cases. Does this > look reasonable ? So far, my testing is fine. What am > I missing here ? Nothing. ext3's writepage(), prepare_write() and commit_write() do often needlessy open and close transactions when we're doing overwrites. It's something I've meant to look at for a few years, on and off. I'd expect that prepare_write() and commit_write() are more important than writepage(). It might be better to test PageMappedToDisk() rather than walking the buffers. It's certainly faster and it makes optimisation of prepare_write() and commit_write() easier to handle. I'm not sure that PageMappedToDisk() gets set in all the right places though - it's mainly for the `nobh' handling and block_prepare_write() would need to be taught to set it. I guess that'd be a net win, even if only ext3 uses it.. Then again, we might be able to speed up block_prepare_write() if PageMappedToDisk(page). If we go this way we need to be very very careful to keep PG_mappedtodisk coherent with the state of the buffers. Tricky. We need to think about whether block_truncate_page() should be clearing PG_mappedtoisk if we did a partial truncate. Don't forget that ext3 supports journalled-mode files on ordered- or writeback-mounted filesystems, via `chattr +j'. Please be sure to test the various combinations which that allows when playing with the write paths - it can trip things up. Also be sure to test nobh-mode.