jbd2: calculate statistics without holding j_state_lock and j_list_lock
The two hottest locks, and thus the biggest scalability bottlenecks,
in the jbd2 layer, are the j_list_lock and j_state_lock. This has
inspired some people to do some truly unnatural things[1].
[1] https://www.usenix.org/system/files/conference/fast14/fast14-paper_kang.pdf
We don't need to be holding both j_state_lock and j_list_lock while
calculating the journal statistics, so move those calculations to the
very end of jbd2_journal_commit_transaction.
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
diff --git a/fs/jbd2/commit.c b/fs/jbd2/commit.c
index 765b31d..af36252 100644
--- a/fs/jbd2/commit.c
+++ b/fs/jbd2/commit.c
@@ -1083,24 +1083,7 @@
atomic_read(&commit_transaction->t_handle_count);
trace_jbd2_run_stats(journal->j_fs_dev->bd_dev,
commit_transaction->t_tid, &stats.run);
-
- /*
- * Calculate overall stats
- */
- spin_lock(&journal->j_history_lock);
- journal->j_stats.ts_tid++;
- if (commit_transaction->t_requested)
- journal->j_stats.ts_requested++;
- journal->j_stats.run.rs_wait += stats.run.rs_wait;
- journal->j_stats.run.rs_request_delay += stats.run.rs_request_delay;
- journal->j_stats.run.rs_running += stats.run.rs_running;
- journal->j_stats.run.rs_locked += stats.run.rs_locked;
- journal->j_stats.run.rs_flushing += stats.run.rs_flushing;
- journal->j_stats.run.rs_logging += stats.run.rs_logging;
- journal->j_stats.run.rs_handle_count += stats.run.rs_handle_count;
- journal->j_stats.run.rs_blocks += stats.run.rs_blocks;
- journal->j_stats.run.rs_blocks_logged += stats.run.rs_blocks_logged;
- spin_unlock(&journal->j_history_lock);
+ stats.ts_requested = (commit_transaction->t_requested) ? 1 : 0;
commit_transaction->t_state = T_COMMIT_CALLBACK;
J_ASSERT(commit_transaction == journal->j_committing_transaction);
@@ -1157,4 +1140,21 @@
spin_unlock(&journal->j_list_lock);
write_unlock(&journal->j_state_lock);
wake_up(&journal->j_wait_done_commit);
+
+ /*
+ * Calculate overall stats
+ */
+ spin_lock(&journal->j_history_lock);
+ journal->j_stats.ts_tid++;
+ journal->j_stats.ts_requested += stats.ts_requested;
+ journal->j_stats.run.rs_wait += stats.run.rs_wait;
+ journal->j_stats.run.rs_request_delay += stats.run.rs_request_delay;
+ journal->j_stats.run.rs_running += stats.run.rs_running;
+ journal->j_stats.run.rs_locked += stats.run.rs_locked;
+ journal->j_stats.run.rs_flushing += stats.run.rs_flushing;
+ journal->j_stats.run.rs_logging += stats.run.rs_logging;
+ journal->j_stats.run.rs_handle_count += stats.run.rs_handle_count;
+ journal->j_stats.run.rs_blocks += stats.run.rs_blocks;
+ journal->j_stats.run.rs_blocks_logged += stats.run.rs_blocks_logged;
+ spin_unlock(&journal->j_history_lock);
}
