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Subject[PATCH 1/4] ext3: enable barriers by default
I can't think of any valid reason for ext3 to not use barriers when
they are available; I believe this is necessary for filesystem
integrity in the face of a volatile write cache on storage.

An administrator who trusts that the cache is sufficiently battery-
backed (and power supplies are sufficiently redundant, etc...)
can always turn it back off again.

SuSE has carried such a patch for quite some time now.

Also document the mount option while we're at it.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Acked-by: Jan Kara <jack@suse.cz>
---
Documentation/filesystems/ext3.txt | 12 ++++++++++--
fs/ext3/super.c | 11 +++++++++--
2 files changed, 19 insertions(+), 4 deletions(-)

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..9c30dc7 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 = sbi->s_journal;
unsigned long def_mount_opts;

def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
@@ -613,8 +614,13 @@ 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");
+ /*
+ * jbd inherits the barrier flag from ext3, and may actually
+ * turn off barriers if a write fails, so it's the real test.
+ */
+ if (!test_opt(sb, BARRIER) ||
+ (journal && !(journal->j_flags & JFS_BARRIER)))
+ seq_puts(seq, ",barrier=0");
if (test_opt(sb, NOBH))
seq_puts(seq, ",nobh");

@@ -1589,6 +1595,7 @@ 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))
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