dont-hold-j_state_lock-during-wake_up

   1 jbd2: don't hold j_state_lock while calling wake_up()
   2
   3 The j_state_lock is one of the hottest locks in the jbd2 layer and
   4 thus one of its scalability bottlenecks.
   5
   6 We don't need to be holding the j_state_lock while we are calling
   7 wake_up(&journal->j_wait_commit), so release the lock a little bit
   8 earlier.
   9
  10 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  11 diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
  12 index 244b6f6..67b8e30 100644
  13 --- a/fs/jbd2/journal.c
  14 +++ b/fs/jbd2/journal.c
  15 @@ -302,8 +302,8 @@ static void journal_kill_thread(journal_t *journal)
  16         journal->j_flags |= JBD2_UNMOUNT;
  17
  18         while (journal->j_task) {
  19 -               wake_up(&journal->j_wait_commit);
  20                 write_unlock(&journal->j_state_lock);
  21 +               wake_up(&journal->j_wait_commit);
  22                 wait_event(journal->j_wait_done_commit, journal->j_task == NULL);
  23                 write_lock(&journal->j_state_lock);
  24         }
  25 @@ -710,8 +710,8 @@ int jbd2_log_wait_commit(journal_t *journal, tid_t tid)
  26         while (tid_gt(tid, journal->j_commit_sequence)) {
  27                 jbd_debug(1, "JBD2: want %d, j_commit_sequence=%d\n",
  28                                   tid, journal->j_commit_sequence);
  29 -               wake_up(&journal->j_wait_commit);
  30                 read_unlock(&journal->j_state_lock);
  31 +               wake_up(&journal->j_wait_commit);
  32                 wait_event(journal->j_wait_done_commit,
  33                                 !tid_gt(tid, journal->j_commit_sequence));
  34                 read_lock(&journal->j_state_lock);