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Commit 571640ca authored by Eric Sandeen's avatar Eric Sandeen Committed by Theodore Ts'o
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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: default avatarEric Sandeen <sandeen@redhat.com>
Signed-off-by: default avatarMingming Cao <cmm@us.ibm.com>
Signed-off-by: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 034772b0

Documentation/filesystems/ext4.txt

+10 −2
Original line number Diff line number Diff line
@@ -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.

fs/ext4/super.c

+9 −2
Original line number Diff line number Diff line
@@ -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