Re: [PATCH 2/2] ext4: Automatically enable journal_async_commit on ext4 file systems

[Eric Sandeen <sandeen@redhat.com>]

Theodore Ts'o wrote:
> Now that we have cleaned up journal_async_commit, it's safe to enable
> it all the time.  But we only want to do so if ext4-specific INCOMPAT
> features are enabled, since otherwise we will prevent the filesystem
> from being mounted using ext3.

Has anyone done some serious power-fail/crash (real or simulated) 
testing with this?  If not, I think we should before it's default...

-Eric

> Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
> ---
>  Documentation/filesystems/ext4.txt |    8 ++++++--
>  fs/ext4/super.c                    |   26 ++++++++++++++++++++++++--
>  2 files changed, 30 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/filesystems/ext4.txt b/Documentation/filesystems/ext4.txt
> index 3e329db..4f8d73a 100644
> --- a/Documentation/filesystems/ext4.txt
> +++ b/Documentation/filesystems/ext4.txt
> @@ -135,8 +135,12 @@ ro                   	Mount filesystem read only. Note that ext4 will
>  		     	writes to the filesystem.
>  
>  journal_async_commit	Commit block can be written to disk without waiting
> -			for descriptor blocks. If enabled older kernels cannot
> -			mount the device.
> +			for descriptor blocks.  This mount option will be 
> +			automatically enabled if ext4-specific INCOMPAT
> +			features are present in the file system.
> +
> +nojournal_async_commit	Disable the journal_async_commit option, even
> +			for ext4 filesystems.
>  
>  journal=update		Update the ext4 file system's journal to the current
>  			format.
> diff --git a/fs/ext4/super.c b/fs/ext4/super.c
> index f1815d3..f644a5c 100644
> --- a/fs/ext4/super.c
> +++ b/fs/ext4/super.c
> @@ -75,6 +75,15 @@ static int ext4_unfreeze(struct super_block *sb);
>  static void ext4_write_super(struct super_block *sb);
>  static int ext4_freeze(struct super_block *sb);
>  
> +/*
> + * If ext4 filesystem features are enabled, then enable async_commits
> + * by default.
> + */
> +#define ASYNC_COMMIT_DEFAULT(sb) (EXT4_HAS_INCOMPAT_FEATURE(sb, \
> +					(EXT4_FEATURE_INCOMPAT_EXTENTS| \
> +					 EXT4_FEATURE_INCOMPAT_64BIT| \
> +					 EXT4_FEATURE_INCOMPAT_FLEX_BG)))
> +
>  
>  ext4_fsblk_t ext4_block_bitmap(struct super_block *sb,
>  			       struct ext4_group_desc *bg)
> @@ -845,8 +854,13 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
>  	 */
>  	seq_puts(seq, ",barrier=");
>  	seq_puts(seq, test_opt(sb, BARRIER) ? "1" : "0");
> -	if (test_opt(sb, JOURNAL_ASYNC_COMMIT))
> -		seq_puts(seq, ",journal_async_commit");
> +	if (ASYNC_COMMIT_DEFAULT(sb)) {
> +		if (!test_opt(sb, JOURNAL_ASYNC_COMMIT))
> +			seq_puts(seq, ",nojournal_async_commit");
> +	} else {
> +		if (test_opt(sb, JOURNAL_ASYNC_COMMIT))
> +			seq_puts(seq, ",journal_async_commit");
> +	}
>  	if (test_opt(sb, NOBH))
>  		seq_puts(seq, ",nobh");
>  	if (test_opt(sb, I_VERSION))
> @@ -1050,6 +1064,7 @@ enum {
>  	Opt_commit, Opt_min_batch_time, Opt_max_batch_time,
>  	Opt_journal_update, Opt_journal_dev,
>  	Opt_journal_checksum, Opt_journal_async_commit,
> +	Opt_nojournal_async_commit,
>  	Opt_abort, Opt_data_journal, Opt_data_ordered, Opt_data_writeback,
>  	Opt_data_err_abort, Opt_data_err_ignore, Opt_mb_history_length,
>  	Opt_usrjquota, Opt_grpjquota, Opt_offusrjquota, Opt_offgrpjquota,
> @@ -1092,6 +1107,7 @@ static const match_table_t tokens = {
>  	{Opt_journal_dev, "journal_dev=%u"},
>  	{Opt_journal_checksum, "journal_checksum"},
>  	{Opt_journal_async_commit, "journal_async_commit"},
> +	{Opt_nojournal_async_commit, "nojournal_async_commit"},
>  	{Opt_abort, "abort"},
>  	{Opt_data_journal, "data=journal"},
>  	{Opt_data_ordered, "data=ordered"},
> @@ -1284,6 +1300,9 @@ static int parse_options(char *options, struct super_block *sb,
>  		case Opt_journal_async_commit:
>  			set_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
>  			break;
> +		case Opt_nojournal_async_commit:
> +			clear_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
> +			break;
>  		case Opt_noload:
>  			set_opt(sbi->s_mount_opt, NOLOAD);
>  			break;
> @@ -2422,6 +2441,9 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
>  	 */
>  	set_opt(sbi->s_mount_opt, DELALLOC);
>  
> +	if (ASYNC_COMMIT_DEFAULT(sb))
> +		set_opt(sbi->s_mount_opt, JOURNAL_ASYNC_COMMIT);
> +
>  	if (!parse_options((char *) data, sb, &journal_devnum,
>  			   &journal_ioprio, NULL, 0))
>  		goto failed_mount;