disable-synchronous-transaction-batching-if-max_batch_time-is-zero

   1 ext4: disable synchronous transaction batching if max_batch_time==0
   2
   3 From: Eric Sandeen <sandeen@redhat.com>
   4
   5 The mount manpage says of the max_batch_time option,
   6
   7         This optimization can be turned off entirely
   8         by setting max_batch_time to 0.
   9
  10 But the code doesn't do that.  So fix the code to do
  11 that.
  12
  13 Signed-off-by: Eric Sandeen <sandeen@redhat.com>
  14 Signed-off-by: Theodore Ts'o <tytso@mit.edu>
  15 Cc: stable@vger.kernel.org
  16 ---
  17
  18 Lightly tested: it mounts, accepts the mount option == 0,
  19 shows "0" in /proc/mounts, and does basic IO & unmounts
  20 without crashing.  ;)
  21
  22 diff --git a/fs/ext4/super.c b/fs/ext4/super.c
  23 index 6f9e6fa..ab5a791 100644
  24 --- a/fs/ext4/super.c
  25 +++ b/fs/ext4/super.c
  26 @@ -1524,8 +1524,6 @@ static int handle_mount_opt(struct super_block *sb, char *opt, int token,
  27                         arg = JBD2_DEFAULT_MAX_COMMIT_AGE;
  28                 sbi->s_commit_interval = HZ * arg;
  29         } else if (token == Opt_max_batch_time) {
  30 -               if (arg == 0)
  31 -                       arg = EXT4_DEF_MAX_BATCH_TIME;
  32                 sbi->s_max_batch_time = arg;
  33         } else if (token == Opt_min_batch_time) {
  34                 sbi->s_min_batch_time = arg;
  35
  36 diff --git a/fs/jbd2/transaction.c b/fs/jbd2/transaction.c
  37 index 38cfcf5..6f0f590 100644
  38 --- a/fs/jbd2/transaction.c
  39 +++ b/fs/jbd2/transaction.c
  40 @@ -1588,9 +1588,12 @@ int jbd2_journal_stop(handle_t *handle)
  41          * to perform a synchronous write.  We do this to detect the
  42          * case where a single process is doing a stream of sync
  43          * writes.  No point in waiting for joiners in that case.
  44 +        *
  45 +        * Setting max_batch_time to 0 disables this completely.
  46          */
  47         pid = current->pid;
  48 -       if (handle->h_sync && journal->j_last_sync_writer != pid) {
  49 +       if (handle->h_sync && journal->j_last_sync_writer != pid &&
  50 +           journal->j_max_batch_time) {
  51                 u64 commit_time, trans_time;
  52
  53                 journal->j_last_sync_writer = pid;
  54
  55 --
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