From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753523Ab1HSRlm (ORCPT ); Fri, 19 Aug 2011 13:41:42 -0400 Received: from oproxy6-pub.bluehost.com ([67.222.54.6]:51890 "HELO oproxy6-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751727Ab1HSRll (ORCPT ); Fri, 19 Aug 2011 13:41:41 -0400 Message-ID: <4E4EA190.7080905@coly.li> Date: Sat, 20 Aug 2011 01:46:56 +0800 From: Coly Li Reply-To: i@coly.li User-Agent: Mozilla/5.0 (X11; U; Linux x86_64; zh-CN; rv:1.9.2.13) Gecko/20101206 SUSE/3.1.7 Thunderbird/3.1.7 MIME-Version: 1.0 To: djwong@us.ibm.com CC: "Theodore Ts'o" , Andreas Dilger , linux-fsdevel , linux-ext4 , linux-kernel , Sunil Mushran , Joel Becker , Mingming Cao , Amir Goldstein , Andi Kleen Subject: Re: [RFC] ext4 metadata checksumming design References: <20110817032519.GN20655@tux1.beaverton.ibm.com> In-Reply-To: <20110817032519.GN20655@tux1.beaverton.ibm.com> X-Enigmail-Version: 1.1.2 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-Identified-User: {1390:box585.bluehost.com:colyli:coly.li} {sentby:smtp auth 118.143.39.4 authed with i@coly.li} Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2011年08月17日 11:25, Darrick J. Wong Wrote: > Hi all, > > I've created a page on the ext4 wiki outlining the patchset that I'm working on > to add metadata checksumming to ext4. The page can be found at this address: > https://ext4.wiki.kernel.org/index.php/Ext4_Metadata_Checksums > Hi Darrick, I just go through the proposal, have on objection for most of the text. Only some things want to confirm, 1) If a metadata_csum enabled file system is metadata_csum disabled, it should be better to mark the block group or inode whether the existing (disabled) checksum is valid or not. So if people re-enable metadata_csum, we can save quite a lot of time to re-build check sums for all metadata objects. 2) In no-journal mode, every time when we modify the metadata objects, we may have to hold a lock, calculate the check sum, and release the lock, which may introduce performance regression. I hope this is only my unnecessary over worry. BTW, an engineer in Taobao kernel team, is trying to count different meta data objects I/O in run time now. One of the first efforts, is trying to unify a set of routines to read or dirty meta data object blocks. A.k.a something (might) like ext4_read_ext_block(), ext4_read_idx_block(), ... etc. Then the counting routines can be added inside the meta data object blocks I/O routines. So far, it seems the modification is not trivial, needs more study on the code. Anyway, since you mentioned on the wiki page, just let you know what we are doing now :-) P.S. The idea of meta data I/O counting is to help us understanding the I/O characteristic of our online servers running Ext4 file systems, which is the basic material for further I/O performance optimization. Thanks. -- Coly Li