From: Jan Kara Subject: Re: [PATCHv6 3/5] ext4: remove unnecessary superblock dirtying Date: Wed, 11 Jul 2012 12:07:26 +0200 Message-ID: <20120711100726.GE1316@quack.suse.cz> References: <1342000698-13556-1-git-send-email-dedekind1@gmail.com> <1342000698-13556-4-git-send-email-dedekind1@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Cc: Theodore Tso , Jan Kara , Linux FS Maling List , Linux Kernel Maling List , Ext4 Mailing List To: Artem Bityutskiy Return-path: Content-Disposition: inline In-Reply-To: <1342000698-13556-4-git-send-email-dedekind1@gmail.com> Sender: linux-kernel-owner@vger.kernel.org List-Id: linux-ext4.vger.kernel.org On Wed 11-07-12 12:58:16, Artem Bityutskiy wrote: > From: Artem Bityutskiy > > This patch changes the '__ext4_handle_dirty_super()' function which submits > the superblock for I/O in the following cases: > > 1. When creating the first large file on a file system without > EXT4_FEATURE_RO_COMPAT_LARGE_FILE feature. > 2. When re-sizing the file-system. > 3. When creating an xattr on a file-system without the > EXT4_FEATURE_COMPAT_EXT_ATTR feature. > 4. When adding or deleting an orphan which happens on every delete operation > (because we update the 's_last_orphan' superblock field). > > If the file-system has journal enabled, the superblock is written via the > journal. We do not modify this path. > > If the file-system has no journal, this function, falls back to just marking > the superblock as dirty using the 's_dirt' superblock flag. This means that it > delays the actual superblock I/O submission by 5 seconds (default setting). > Namely, the 'sync_supers()' kernel thread will call 'ext4_write_super()' later > and will actually submit the superblock for I/O. > > And this is the behavior this patch modifies: we stop using 's_dirt' and just > mark the superblock buffer as dirty right away. Indeed: > > 1. It does not add any value to delay the I/O submission for cases 1-3 above. > They are rare. > 2. Case number 4 above depends on whether we have file-system checksumming > enabled or disables. > a) If it is disabled (most common scenario), then it is all-right to just > mark the superblock buffer as dirty right away and it should affect > performance. > b) If it is enabled, then we'll end up doing a bit more work on deletion > because we'll re-calculate superblock checksum every time. > > So case 2.b is a bit controversial, but I think it is acceptable. After all, by > enabling checksumming we already sign up for paying the price of calculating > it. The way to improve checksumming performance globally would be to calculate > it just before sending buffers to the I/O queue. We'd need some kind of > call-back which could be registered by file-systems. > > This patch also removes 's_dirt' condition on the unmount path because we never > set it anymore, so we should not test it. > > Tested using xfstests for both journalled and non-journalled ext4. > > Signed-off-by: Artem Bityutskiy Looks good. Thanks for doing this work! You can add: Reviewed-by: Jan Kara Honza > --- > fs/ext4/ext4_jbd2.c | 5 ++--- > fs/ext4/super.c | 2 +- > 2 files changed, 3 insertions(+), 4 deletions(-) > > diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c > index 90f7c2e..c19ab6a 100644 > --- a/fs/ext4/ext4_jbd2.c > +++ b/fs/ext4/ext4_jbd2.c > @@ -151,11 +151,10 @@ int __ext4_handle_dirty_super(const char *where, unsigned int line, > if (err) > ext4_journal_abort_handle(where, line, __func__, > bh, handle, err); > - } else if (now) { > + } else { > ext4_superblock_csum_set(sb, > (struct ext4_super_block *)bh->b_data); > mark_buffer_dirty(bh); > - } else > - sb->s_dirt = 1; > + } > return err; > } > diff --git a/fs/ext4/super.c b/fs/ext4/super.c > index eb7aa3e..a391c53 100644 > --- a/fs/ext4/super.c > +++ b/fs/ext4/super.c > @@ -896,7 +896,7 @@ static void ext4_put_super(struct super_block *sb) > EXT4_CLEAR_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_RECOVER); > es->s_state = cpu_to_le16(sbi->s_mount_state); > } > - if (sb->s_dirt || !(sb->s_flags & MS_RDONLY)) > + if (!(sb->s_flags & MS_RDONLY)) > ext4_commit_super(sb, 1); > > if (sbi->s_proc) { > -- > 1.7.7.6 > -- Jan Kara SUSE Labs, CR