On Wed 11-07-12 12:58:16, Artem Bityutskiy wrote:
> From: Artem Bityutskiy <artem.bityutskiy@xxxxxxxxxxxxxxx>
>
> 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 <artem.bityutskiy@xxxxxxxxxxxxxxx>
Looks good. Thanks for doing this work! You can add:
Reviewed-by: Jan Kara <jack@xxxxxxx>
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 <jack@xxxxxxx>
SUSE Labs, CR
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