From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-11.2 required=3.0 tests=BAYES_00, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 97370C388F2 for ; Thu, 22 Oct 2020 13:09:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 500E224182 for ; Thu, 22 Oct 2020 13:09:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2899361AbgJVNJP (ORCPT ); Thu, 22 Oct 2020 09:09:15 -0400 Received: from mx2.suse.de ([195.135.220.15]:45234 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2899358AbgJVNJP (ORCPT ); Thu, 22 Oct 2020 09:09:15 -0400 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.221.27]) by mx2.suse.de (Postfix) with ESMTP id 92362AF16; Thu, 22 Oct 2020 13:09:13 +0000 (UTC) Received: by quack2.suse.cz (Postfix, from userid 1000) id 468901E1342; Thu, 22 Oct 2020 15:09:08 +0200 (CEST) Date: Thu, 22 Oct 2020 15:09:08 +0200 From: Jan Kara To: harshad shirwadkar Cc: Jan Kara , Ext4 Developers List , "Theodore Y. Ts'o" Subject: Re: [PATCH v10 2/9] ext4: add fast_commit feature and handling for extended mount options Message-ID: <20201022130908.GD24163@quack2.suse.cz> References: <20201015203802.3597742-1-harshadshirwadkar@gmail.com> <20201015203802.3597742-3-harshadshirwadkar@gmail.com> <20201021161814.GC25702@quack2.suse.cz> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Precedence: bulk List-ID: X-Mailing-List: linux-ext4@vger.kernel.org On Wed 21-10-20 10:31:48, harshad shirwadkar wrote: > On Wed, Oct 21, 2020 at 9:18 AM Jan Kara wrote: > > > > On Thu 15-10-20 13:37:54, Harshad Shirwadkar wrote: > > > We are running out of mount option bits. Add handling for using > > > s_mount_opt2. Add ext4 and jbd2 fast commit feature flag and also add > > > ability to turn off the fast commit feature in Ext4. > > > > > > Signed-off-by: Harshad Shirwadkar > > > --- > > > fs/ext4/ext4.h | 4 ++++ > > > fs/ext4/super.c | 27 ++++++++++++++++++++++----- > > > include/linux/jbd2.h | 5 ++++- > > > 3 files changed, 30 insertions(+), 6 deletions(-) > > > > > > diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h > > > index 1879531a119f..02d7dc378505 100644 > > > --- a/fs/ext4/ext4.h > > > +++ b/fs/ext4/ext4.h > > > @@ -1213,6 +1213,8 @@ struct ext4_inode_info { > > > #define EXT4_MOUNT2_EXPLICIT_JOURNAL_CHECKSUM 0x00000008 /* User explicitly > > > specified journal checksum */ > > > > > > +#define EXT4_MOUNT2_JOURNAL_FAST_COMMIT 0x00000010 /* Journal fast commit */ > > > + > > > #define clear_opt(sb, opt) EXT4_SB(sb)->s_mount_opt &= \ > > > ~EXT4_MOUNT_##opt > > > #define set_opt(sb, opt) EXT4_SB(sb)->s_mount_opt |= \ > > > @@ -1813,6 +1815,7 @@ static inline bool ext4_verity_in_progress(struct inode *inode) > > > #define EXT4_FEATURE_COMPAT_RESIZE_INODE 0x0010 > > > #define EXT4_FEATURE_COMPAT_DIR_INDEX 0x0020 > > > #define EXT4_FEATURE_COMPAT_SPARSE_SUPER2 0x0200 > > > +#define EXT4_FEATURE_COMPAT_FAST_COMMIT 0x0400 > > > #define EXT4_FEATURE_COMPAT_STABLE_INODES 0x0800 > > > > Is fast commit really a compat feature? IMO if there are fast commits > > stored in the journal, the filesystem is actually incompatible with the > > old kernels because data we guranteed to be permanenly stored may be > > invisible for the old kernel (since it won't replay fastcommit > > transactions). > > > > ... > > > > Oh, now I see that the journal FAST_COMMIT is actually incompat. So what's > > the point of compat ext4 feature with incompat JBD2 feature? > So having fast commits enabled on an ext4 file system doesn't > immediately make it incompatible with the older kernels. FS becomes > incompatible only if there are fast commits blocks that are stored in > the journal. So, one of the tricks that this patchset does is on a > clean unmount, since it's guaranteed that there are no fast commit > blocks in journal, we clear out the JBD2 incompat flag and preserve > the compat flag in ext4. So, we can think of ext4 compat flag as "FS > will try fast commits when possible" while jbd2 incompat flag as > "There are fast commits blocks present in the journal". Does that make > sense? Yes, understood. That's clever. Thanks for explanation! But please add the above justification to the description of EXT4_FEATURE_COMPAT_FAST_COMMIT feature or somewhere around that. Honza -- Jan Kara SUSE Labs, CR