bcachefs: Skip periodic wakeup of journal reclaim when journal empty

Less system noise.
Signed-off-by: Kent Overstreet <kent.overstreet@gmail.com>

fs/bcachefs/journal.c

@@ -240,6 +240,9 @@ static int journal_entry_open(struct journal *j)
 	if (u64s <= 0)
 		return cur_entry_journal_full;
 
+	if (fifo_empty(&j->pin) && j->reclaim_thread)
+		wake_up_process(j->reclaim_thread);
+
 	/*
 	 * The fifo_push() needs to happen at the same time as j->seq is
 	 * incremented for journal_last_seq() to be calculated correctly

fs/bcachefs/journal_reclaim.c

@@ -667,6 +667,7 @@ static int bch2_journal_reclaim_thread(void *arg)
 	struct journal *j = arg;
 	struct bch_fs *c = container_of(j, struct bch_fs, journal);
 	unsigned long delay, now;
+	bool journal_empty;
 	int ret = 0;
 
 	set_freezable();
@@ -693,10 +694,17 @@ static int bch2_journal_reclaim_thread(void *arg)
 				break;
 			if (j->reclaim_kicked)
 				break;
-			if (time_after_eq(jiffies, j->next_reclaim))
-				break;
-			schedule_timeout(j->next_reclaim - jiffies);
 
+			spin_lock(&j->lock);
+			journal_empty = fifo_empty(&j->pin);
+			spin_unlock(&j->lock);
+
+			if (journal_empty)
+				schedule();
+			else if (time_after(j->next_reclaim, jiffies))
+				schedule_timeout(j->next_reclaim - jiffies);
+			else
+				break;
 		}
 		__set_current_state(TASK_RUNNING);
 	}

fs/bcachefs/journal_types.h

@@ -243,6 +243,10 @@ struct journal {
 	spinlock_t		err_lock;
 
 	struct mutex		reclaim_lock;
+	/*
+	 * Used for waiting until journal reclaim has freed up space in the
+	 * journal:
+	 */
 	wait_queue_head_t	reclaim_wait;
 	struct task_struct	*reclaim_thread;
 	bool			reclaim_kicked;