ext4: Clean up s_dirt handling

We don't need to set s_dirt in most of the ext4 code when journaling
is enabled.  In ext3/4 some of the summary statistics for # of free
inodes, blocks, and directories are calculated from the per-block
group statistics when the file system is mounted or unmounted.  As a
result the superblock doesn't have to be updated, either via the
journal or by setting s_dirt.  There are a few exceptions, most
notably when resizing the file system, where the superblock needs to
be modified --- and in that case it should be done as a journalled
operation if possible, and s_dirt set only in no-journal mode.

This patch will optimize out some unneeded disk writes when using ext4
with a journal.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>

1 files changed, 16 insertions, 0 deletions

diff --git a/fs/ext4/ext4_jbd2.c b/fs/ext4/ext4_jbd2.c
index 53d2764..cfd27b3 100644
--- a/fs/ext4/ext4_jbd2.c
+++ b/fs/ext4/ext4_jbd2.c
@@ -143,3 +143,19 @@ int __ext4_handle_dirty_metadata(const char *where, handle_t *handle,
 	}
 	return err;
 }
+
+int __ext4_handle_dirty_super(const char *where, handle_t *handle,
+			      struct super_block *sb)
+{
+	struct buffer_head *bh = EXT4_SB(sb)->s_sbh;
+	int err = 0;
+
+	if (ext4_handle_valid(handle)) {
+		err = jbd2_journal_dirty_metadata(handle, bh);
+		if (err)
+			ext4_journal_abort_handle(where, __func__, bh,
+						  handle, err);
+	} else
+		sb->s_dirt = 1;
+	return err;
+}