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ext4: enable barriers by default 

I can't think of any valid reason for ext4 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 ext3 for quite some time now.

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

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
This commit is contained in:
Eric Sandeen 2008-05-26 12:29:46 -04:00 коммит произвёл Theodore Ts'o
Родитель 034772b068
Коммит 571640cad3
2 изменённых файлов: 19 добавлений и 4 удалений
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12
Documentation/filesystems/ext4.txt
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@ -139,8 +139,16 @@ commit=nrsec (*) Ext4 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.

11
fs/ext4/super.c
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@ -671,6 +671,7 @@ static int ext4_show_options(struct seq_file *seq, struct vfsmount *vfs)
unsigned long def_mount_opts;
struct super_block *sb = vfs->mnt_sb;
struct ext4_sb_info *sbi = EXT4_SB(sb);
journal_t *journal = sbi->s_journal;
struct ext4_super_block *es = sbi->s_es;
def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
@ -729,8 +730,13 @@ static int ext4_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");
/*
* We're changing the default of barrier mount option, so
* let's always display its mount state so it's clear what its
* status is.
*/
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 (test_opt(sb, NOBH))
@ -1909,6 +1915,7 @@ static int ext4_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);
/*
* turn on extents feature by default in ext4 filesystem