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

[Ric Wheeler <ricwheeler@xxxxxxxxx>]

Eric Sandeen wrote:
> 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

I think that we also need to see some very compelling performance 
numbers to justify the complexity. Journaling is complex enough, so if 
this is not a win, we should (in my opinion) go with the simplest 
technique :-)

ric

> > Signed-off-by: "Theodore Ts'o" <tytso@xxxxxxx>
> > ---
> >  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;
>
> --
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