Commit 42cf3452 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

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: default avatar"Theodore Ts'o" <tytso@mit.edu>
parent 3469a32a

fs/jbd2/commit.c

+18 −18
Original line number Diff line number Diff line
@@ -1083,24 +1083,7 @@ restart_loop: 
		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 @@ restart_loop: 
	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);

}

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