ext4: disable synchronous transaction batching if max_batch_time==0

The mount manpage says of the max_batch_time option,

	This optimization can be turned off entirely
	by setting max_batch_time to 0.

But the code doesn't do that.  So fix the code to do
that.

Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
Cc: stable@vger.kernel.org

2 files changed, 4 insertions, 3 deletions

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 342394772b6c..6297c07c937f 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1525,8 +1525,6 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
                         arg = JBD2_DEFAULT_MAX_COMMIT_AGE;
                 sbi->s_commit_interval = HZ * arg;
         } else if (token == Opt_max_batch_time) {
-                if (arg == 0)
-                        arg = EXT4_DEF_MAX_BATCH_TIME;
                 sbi->s_max_batch_time = arg;
         } else if (token == Opt_min_batch_time) {
                 sbi->s_min_batch_time = arg;
diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
index 38cfcf5f6fce..6f0f590cc5a3 100644
--- a/fs/jbd2/transaction.c
+++ b/fs/jbd2/transaction.c
@@ -1588,9 +1588,12 @@ int jbd2_journal_stop(handle_t *handle)
          * to perform a synchronous write.  We do this to detect the
          * case where a single process is doing a stream of sync
          * writes.  No point in waiting for joiners in that case.
+         *
+         * Setting max_batch_time to 0 disables this completely.
          */
         pid = current->pid;
-        if (handle->h_sync && journal->j_last_sync_writer != pid) {
+        if (handle->h_sync && journal->j_last_sync_writer != pid &&
+            journal->j_max_batch_time) {
                 u64 commit_time, trans_time;
 
                 journal->j_last_sync_writer = pid;