From mboxrd@z Thu Jan 1 00:00:00 1970 From: Badari Pulavarty Subject: Re: [Ext2-devel] Reviewing ext3 improvement patches (delalloc, mballoc, extents) Date: 03 Mar 2005 17:12:14 -0800 Message-ID: <1109898734.4961.11.camel@dyn318077bld.beaverton.ibm.com> References: <20050303083349.GA4896@in.ibm.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: ext2-devel , linux-fsdevel@vger.kernel.org, Alex Tomas Received: from e33.co.us.ibm.com ([32.97.110.131]:27571 "EHLO e33.co.us.ibm.com") by vger.kernel.org with ESMTP id S262838AbVCDBOs (ORCPT ); Thu, 3 Mar 2005 20:14:48 -0500 Received: from d03relay05.boulder.ibm.com (d03relay05.boulder.ibm.com [9.17.195.107]) by e33.co.us.ibm.com (8.12.10/8.12.9) with ESMTP id j241Ej0D674860 for ; Thu, 3 Mar 2005 20:14:45 -0500 Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by d03relay05.boulder.ibm.com (8.12.10/NCO/VER6.6) with ESMTP id j241Ejwp205700 for ; Thu, 3 Mar 2005 18:14:45 -0700 Received: from d03av03.boulder.ibm.com (loopback [127.0.0.1]) by d03av03.boulder.ibm.com (8.12.11/8.12.11) with ESMTP id j241Ei3W015047 for ; Thu, 3 Mar 2005 18:14:45 -0700 To: suparna@in.ibm.com In-Reply-To: <20050303083349.GA4896@in.ibm.com> Sender: linux-fsdevel-owner@vger.kernel.org List-Id: linux-fsdevel.vger.kernel.org On Thu, 2005-03-03 at 00:33, Suparna Bhattacharya wrote: > Since the performance improvements seen so far are quite encouraging, > and momentum is picking up so well, I started looking through the > patches from Alex ... just a quick code walkthrough to get a hang > of it and think about what kind of simplifications might be possible > and what it might take for inclusion. > > I haven't had a chance to go too deep line by line yet, > but thought I'd initiate some discussion with some first impressions > and summary of what directions I hear several people converging > towards to validate if I'm on the right track here. > > diffstat of the 3 patches : 22 files changed, 5920 insertions(+), > 47 deletions. The largest is in the extents patch (2743), mballoc > is 1968, and delalloc is 1209. To use delalloc, which gives us > all the performance benefits, right now we need all the 3 patches > to be used in conjunction. Supporting extent map btrees as well > as traditional indexing and associated options for compatibility etc > is perhaps the more invasive of changes. Given that keeping ext3 > stable and maintainable is a key concern (that is after all a major > reason why a lot of users rely on ext3), a somewhat incremental > approach is desirable. > > So, I'll start from the direction that has been suggested by > some -- (1) delayed allocation without changing the > on-disk format. And then later (2) go on to breaking format with > all changes for scalability to larger files with full extents > support (haven't thought enough about this yet - maybe in a > separate mail) > Just doing delayed allocation without multiblock allocation (with the current layout) is not really a useful thing, IMHO. We will benifit few cases, but in general - we moved the block allocation overhead from prepare write to writepages/writepage time. There is a little benifit of not doing journaling twice etc.. but I don't think it would be enough to justify the effort. Isn't it ? So, may be we should look at adding multiblock allocation + delayed allocation to current ext3 layout. Then we can evaluate the benifits of having "extents" etc and then break the layout ? One more thing, we need to keep in mind is - we need to make sure that "ordered" mode also improved - since all our testcode focuses on "writeback" mode and the default mode is "ordered" :( Thanks, Badari