From: Joel Becker Subject: Re: [PATCH 0/2] Add inode checksum support to ext4 Date: Fri, 29 Jul 2011 06:19:38 -0700 Message-ID: <20110729131937.GB5910@noexit.corp.google.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> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: "Darrick J. Wong" , Andreas Dilger , Mingming Cao , Theodore Ts'o , linux-ext4 , linux-kernel To: Andreas Dilger Return-path: Received: from zeniv.linux.org.uk ([195.92.253.2]:59606 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750901Ab1G2NT6 (ORCPT ); Fri, 29 Jul 2011 09:19:58 -0400 Content-Disposition: inline In-Reply-To: <0E795C1D-AD1E-4CC4-9426-2B58D98B14DC@dilger.ca> Sender: linux-ext4-owner@vger.kernel.org List-ID: 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 acceleration > 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 course we added the triggers to jbd2 so we only have to do the calculations on read and write. > Yes, it makes sense to just put a "fake" dirent at the end of the leaf block, > or similar. I don't think it is necessary to modify existing directories or > extent blocks to add these structures in, if there is no room, but for new > blocks, or blocks with space it is enough. We have tunefs.ocfs2 code to adjust existing directories to add the trailer. It's not too bad, really. Joel -- "People with narrow minds usually have broad tongues." http://www.jlbec.org/ jlbec@evilplan.org