On Thu 15-05-08 15:44:04, Eric Sandeen wrote:
> Jan Kara wrote:
>
> >> As I look at my shiny new 500G disks with 32MB of cache, I find myself
> >> wondering why the default for ext3 and ext4 is to have barriers disabled.
> >>
> >> This is a pretty dangerous default w.r.t. filesystem integrity on power
> >> loss, no?
> >>
> > JFYI: SUSE kernel carries for ages a patch which changes this default.
> > I'd be more than happy to drop it ;).
> >
> > Honza
> >
> What do folks think of this?
>
> the show_options change is a little funky since jbd may do a test
> write and fail... (actually I was thinking maybe at fill_super we
> should do a test barrier write and get it out of the way early...)
Yes, the patch looks fine with me.
Acked-by: Jan Kara <jack@xxxxxxx>
> diff --git a/Documentation/filesystems/ext3.txt b/Documentation/filesystems/ext3.txt
> index b45f3c1..daab1f5 100644
> --- a/Documentation/filesystems/ext3.txt
> +++ b/Documentation/filesystems/ext3.txt
> @@ -52,8 +52,16 @@ commit=nrsec (*) Ext3 can be told to sync all its data and metadata
> Setting it to very large values will improve
> performance.
>
> -barrier=1 This enables/disables barriers. barrier=0 disables
> - it, barrier=1 enables it.
> +barrier=<0|1(*)> This enables/disables the use of write barriers in
> + the jbd code. barrier=0 disables, barrier=1 enables.
> + This also requires an IO stack which can support
> + barriers, and if jbd gets an error on a barrier
> + write, it will disable again with a warning.
> + Write barriers enforce proper on-disk ordering
> + of journal commits, making volatile disk write caches
> + safe to use, at some performance penalty. If
> + your disks are battery-backed in one way or another,
> + disabling barriers may safely improve performance.
>
> orlov (*) This enables the new Orlov block allocator. It is
> enabled by default.
> diff --git a/fs/ext3/super.c b/fs/ext3/super.c
> index fe3119a..d06e0f3 100644
> --- a/fs/ext3/super.c
> +++ b/fs/ext3/super.c
> @@ -555,6 +555,7 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs)
> struct super_block *sb = vfs->mnt_sb;
> struct ext3_sb_info *sbi = EXT3_SB(sb);
> struct ext3_super_block *es = sbi->s_es;
> + journal_t *journal = EXT3_SB(sb)->s_journal;
> unsigned long def_mount_opts;
>
> def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
> @@ -613,8 +614,16 @@ static int ext3_show_options(struct seq_file *seq, struct vfsmount *vfs)
> seq_printf(seq, ",commit=%u",
> (unsigned) (sbi->s_commit_interval / HZ));
> }
> - if (test_opt(sb, BARRIER))
> - seq_puts(seq, ",barrier=1");
> + if (!test_opt(sb, BARRIER)) {
> + seq_puts(seq, ",barrier=0");
> + } else {
> + /*
> + * jbd inherits the barrier flag from ext3, and jbd may actually
> + * turn off barriers if a write fails, so it's the real test.
> + */
> + if (journal && !(journal->j_flags & JFS_BARRIER))
> + seq_puts(seq, ",barrier=1(failed)");
> + }
> if (test_opt(sb, NOBH))
> seq_puts(seq, ",nobh");
>
> @@ -1589,6 +1598,7 @@ static int ext3_fill_super (struct super_block *sb, void *data, int silent)
> sbi->s_resgid = le16_to_cpu(es->s_def_resgid);
>
> set_opt(sbi->s_mount_opt, RESERVATION);
> + set_opt(sbi->s_mount_opt, BARRIER);
>
> if (!parse_options ((char *) data, sb, &journal_inum, &journal_devnum,
> NULL, 0))
>
--
Jan Kara <jack@xxxxxxx>
SUSE Labs, CR
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