From: Coly Li Subject: Re: [PATCH 0/2] Add inode checksum support to ext4 Date: Mon, 01 Aug 2011 15:16:30 +0800 Message-ID: <4E3652CE.1060000@coly.li> 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> Reply-To: i@coly.li 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 oproxy9.bluehost.com ([69.89.24.6]:41137 "HELO oproxy9.bluehost.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with SMTP id S1751467Ab1HAHMP (ORCPT ); Mon, 1 Aug 2011 03:12:15 -0400 In-Reply-To: <20110801050435.GC5716@noexit.corp.google.com> Sender: linux-ext4-owner@vger.kernel.org List-ID: On 2011=E5=B9=B408=E6=9C=8801=E6=97=A5 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=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: >>>>> 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_*() func= tions >>>> 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 ne= w 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 n= o >> danger of a set-bit-after-last-checksum. But you will have to lock >> around the checksum calculation in non-journaling mode. JBD2 handle= s it >> for journaling mode. >=20 > 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(). >=20 Yes, you are right. What I worried was inode bitmap, because last time (before uninit_bg wa= s developed), inode bitmap was set by ext4_set_bit_atomic(). Now I see inode bitmap is set by ext4_claim_inod= e() 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. --=20 Coly Li -- 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