jbd2-calc-stats-wo-j_state_lock-and-j_list_lock

   1 jbd2: calculate statistics without holding j_state_lock and j_list_lock
   2
   3 The two hottest locks, and thus the biggest scalability bottlenecks,
   4 in the jbd2 layer, are the j_list_lock and j_state_lock.  This has
   5 inspired some people to do some truly unnatural things[1].
   6
   7 [1] https://www.usenix.org/system/files/conference/fast14/fast14-paper_kang.pdf
   8
   9 We don't need to be holding both j_state_lock and j_list_lock while
  10 calculating the journal statistics, so move those calculations to the
  11 very end of jbd2_journal_commit_transaction.
  12
  13 Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
  14
  15 diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
  16 index 765b31d..af36252 100644
  17 --- a/fs/jbd2/commit.c
  18 +++ b/fs/jbd2/commit.c
  19 @@ -1083,24 +1083,7 @@ restart_loop:
  20                 atomic_read(&commit_transaction->t_handle_count);
  21         trace_jbd2_run_stats(journal->j_fs_dev->bd_dev,
  22                              commit_transaction->t_tid, &stats.run);
  23 -
  24 -       /*
  25 -        * Calculate overall stats
  26 -        */
  27 -       spin_lock(&journal->j_history_lock);
  28 -       journal->j_stats.ts_tid++;
  29 -       if (commit_transaction->t_requested)
  30 -               journal->j_stats.ts_requested++;
  31 -       journal->j_stats.run.rs_wait += stats.run.rs_wait;
  32 -       journal->j_stats.run.rs_request_delay += stats.run.rs_request_delay;
  33 -       journal->j_stats.run.rs_running += stats.run.rs_running;
  34 -       journal->j_stats.run.rs_locked += stats.run.rs_locked;
  35 -       journal->j_stats.run.rs_flushing += stats.run.rs_flushing;
  36 -       journal->j_stats.run.rs_logging += stats.run.rs_logging;
  37 -       journal->j_stats.run.rs_handle_count += stats.run.rs_handle_count;
  38 -       journal->j_stats.run.rs_blocks += stats.run.rs_blocks;
  39 -       journal->j_stats.run.rs_blocks_logged += stats.run.rs_blocks_logged;
  40 -       spin_unlock(&journal->j_history_lock);
  41 +       stats.ts_requested = (commit_transaction->t_requested) ? 1 : 0;
  42
  43         commit_transaction->t_state = T_COMMIT_CALLBACK;
  44         J_ASSERT(commit_transaction == journal->j_committing_transaction);
  45 @@ -1157,4 +1140,21 @@ restart_loop:
  46         spin_unlock(&journal->j_list_lock);
  47         write_unlock(&journal->j_state_lock);
  48         wake_up(&journal->j_wait_done_commit);
  49 +
  50 +       /*
  51 +        * Calculate overall stats
  52 +        */
  53 +       spin_lock(&journal->j_history_lock);
  54 +       journal->j_stats.ts_tid++;
  55 +       journal->j_stats.ts_requested += stats.ts_requested;
  56 +       journal->j_stats.run.rs_wait += stats.run.rs_wait;
  57 +       journal->j_stats.run.rs_request_delay += stats.run.rs_request_delay;
  58 +       journal->j_stats.run.rs_running += stats.run.rs_running;
  59 +       journal->j_stats.run.rs_locked += stats.run.rs_locked;
  60 +       journal->j_stats.run.rs_flushing += stats.run.rs_flushing;
  61 +       journal->j_stats.run.rs_logging += stats.run.rs_logging;
  62 +       journal->j_stats.run.rs_handle_count += stats.run.rs_handle_count;
  63 +       journal->j_stats.run.rs_blocks += stats.run.rs_blocks;
  64 +       journal->j_stats.run.rs_blocks_logged += stats.run.rs_blocks_logged;
  65 +       spin_unlock(&journal->j_history_lock);
  66  }