From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752373Ab1HAHMW (ORCPT ); Mon, 1 Aug 2011 03:12:22 -0400 Received: from oproxy9.bluehost.com ([69.89.24.6]:45938 "HELO oproxy9.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751891Ab1HAHMP (ORCPT ); Mon, 1 Aug 2011 03:12:15 -0400 Message-ID: <4E3652CE.1060000@coly.li> Date: Mon, 01 Aug 2011 15:16:30 +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: Andreas Dilger , "Darrick J. Wong" , Andreas Dilger , Mingming Cao , "Theodore Ts'o" , linux-ext4 , linux-kernel Subject: Re: [PATCH 0/2] Add inode checksum support to ext4 References: <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> <4E35EAC9.6070707@gmail.com> <20110801045710.GB5716@noexit.corp.google.com> <20110801050435.GC5716@noexit.corp.google.com> In-Reply-To: <20110801050435.GC5716@noexit.corp.google.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 114.251.86.0 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01日 13:04, Joel Becker Wrote: > On Sun, Jul 31, 2011 at 09:57:11PM -0700, Joel Becker wrote: >> On Mon, Aug 01, 2011 at 07:52:41AM +0800, Coly Li wrote: >>> On 2011年07月31日 15:08, Joel Becker Wrote: >>>> On Sat, Jul 30, 2011 at 03:25:32PM +0800, Coly Li wrote: >>>>> 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... >>>> >>>> Sure, but you could use a trigger in journaled mode and then do >>>> the checksums directly in the __ext4_handle_journal_dirty_*() functions >>>> in non-journaled mode. Sure, it would be a little more CPU time, but >>>> the user picked "checksums + no journal" at mkfs time. >>>> >>> >>> 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 bit setting after check sum is calculated. >> >> Every place that changes the bits will eventually call >> ext4_journal_dirty(), which recalculates the checksum. So there's no >> danger of a set-bit-after-last-checksum. But you will have to lock >> around the checksum calculation in non-journaling mode. JBD2 handles it >> for journaling mode. > > Wait, bitsetting in ext4 can't be non-locking. Or are they > crazily stomping on memory? I sure see an assert_spin_locked() in > mb_mark_used(). > Yes, you are right. What I worried was inode bitmap, because last time (before uninit_bg was developed), inode bitmap was set by ext4_set_bit_atomic(). Now I see inode bitmap is set by ext4_claim_inode() which locks the group internally. And I confirm block bitmap is protected by ext4_{lock,unlock}_group(). So there is no risk for set-bit-after-last-checksum. Thanks for the clarification. -- Coly Li