From: Coly Li Subject: Re: [PATCH 0/2] Add inode checksum support to ext4 Date: Mon, 01 Aug 2011 07:52:41 +0800 Message-ID: <4E35EAC9.6070707@gmail.com> References: <20110406224410.GB24354@tux1.beaverton.ibm.com> <1302290868.4461.7.camel@mingming-laptop> <20110727082730.GG20655@tux1.beaverton.ibm.com> <20110728165615.GI20655@tux1.beaverton.ibm.com> <20110728220735.GA27253@noexit.corp.google.com> <0E795C1D-AD1E-4CC4-9426-2B58D98B14DC@dilger.ca> <20110729131937.GB5910@noexit.corp.google.com> <4E33B1EC.9030004@gmail.com> <20110731070832.GA2848@noexit.corp.google.com> Reply-To: colyli@gmail.com Mime-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: QUOTED-PRINTABLE To: Andreas Dilger , "Darrick J. Wong" , Andreas Dilger , Mingming Cao , Theodore Ts'o , l Return-path: Received: from oproxy1-pub.bluehost.com ([66.147.249.253]:53556 "HELO oproxy1-pub.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1753063Ab1GaXsZ (ORCPT ); Sun, 31 Jul 2011 19:48:25 -0400 In-Reply-To: <20110731070832.GA2848@noexit.corp.google.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2011=E5=B9=B407=E6=9C=8831=E6=97=A5 15:08, Joel Becker Wrote: > On Sat, Jul 30, 2011 at 03:25:32PM +0800, Coly Li wrote: >> On 2011=E5=B9=B407=E6=9C=8829=E6=97=A5 21:19, Joel Becker Wrote: >>> On Fri, Jul 29, 2011 at 03:48:45AM -0600, Andreas Dilger wrote: >>>> On 2011-07-28, at 4:07 PM, Joel Becker wrote: >>>>> We use ethernet crc32 in ocfs2. btrfs uses crc32c. Frankly, I >>>>> could have used crc32c if I'd really thought about the hardware >>>>> acceleration benefits. I think it's a good idea for ext4. >>>> >>>> The problem with crc32[c] is that if you don't have hardware accel= eration >>>> it is terribly slow. >>> >>> We find ethernet crc32 just fine in ocfs2. I use the kernel's >>> implementation, which survives everyone's network traffic, and of c= ourse >>> we added the triggers to jbd2 so we only have to do the calculation= s on >>> read and write. >>> >> >> Ext4 supports non-journal mode, and there are a few users (Google, T= aobao, etc.). >> A trigger of jbd2 may not work well for non-journal Ext4 ... >> >> And in non-journal mode, there is not copy of any meta data block in= jbd2, we need to be >> more careful in check summing, e.g. inode/block bitmap blocks... >=20 > Sure, but you could use a trigger in journaled mode and then do > the checksums directly in the __ext4_handle_journal_dirty_*() functio= ns > in non-journaled mode. Sure, it would be a little more CPU time, but > the user picked "checksums + no journal" at mkfs time. >=20 Yes, my idea was similar to you. One thing not clear to me is, in non-journal mode, how to make the page= of bitmap block being stable. Because bits setting in Ext4 bitmap is non-locking, it might be possible that new bi= t setting after check sum is calculated. Coly -- To unsubscribe from this list: send the line "unsubscribe linux-ext4" i= n the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html