md/r5cache: run_no_space_stripes() when R5C_LOG_CRITICAL == 0

With writeback cache, we define log space critical as

   free_space < 2 * reclaim_required_space

So the deassert of R5C_LOG_CRITICAL could happen when
  1. free_space increases
  2. reclaim_required_space decreases

Currently, run_no_space_stripes() is called when 1 happens, but
not (always) when 2 happens.

With this patch, run_no_space_stripes() is call when
R5C_LOG_CRITICAL is cleared.
Signed-off-by: Song Liu <songliubraving@fb.com>
Signed-off-by: Shaohua Li <shli@fb.com>

drivers/md/raid5-cache.c

@@ -370,6 +370,7 @@ static inline void r5c_update_log_state(struct r5l_log *log)
 	struct r5conf *conf = log->rdev->mddev->private;
 	sector_t free_space;
 	sector_t reclaim_space;
+	bool wake_reclaim = false;
 
 	if (!r5c_is_writeback(log))
 		return;
@@ -379,12 +380,18 @@ static inline void r5c_update_log_state(struct r5l_log *log)
 	reclaim_space = r5c_log_required_to_flush_cache(conf);
 	if (free_space < 2 * reclaim_space)
 		set_bit(R5C_LOG_CRITICAL, &conf->cache_state);
-	else
+	else {
+		if (test_bit(R5C_LOG_CRITICAL, &conf->cache_state))
+			wake_reclaim = true;
 		clear_bit(R5C_LOG_CRITICAL, &conf->cache_state);
+	}
 	if (free_space < 3 * reclaim_space)
 		set_bit(R5C_LOG_TIGHT, &conf->cache_state);
 	else
 		clear_bit(R5C_LOG_TIGHT, &conf->cache_state);
+
+	if (wake_reclaim)
+		r5l_wake_reclaim(log, 0);
 }
 
 /*
@@ -1345,6 +1352,10 @@ static void r5c_do_reclaim(struct r5conf *conf)
 		spin_unlock(&conf->device_lock);
 		spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
 	}
+
+	if (!test_bit(R5C_LOG_CRITICAL, &conf->cache_state))
+		r5l_run_no_space_stripes(log);
+
 	md_wakeup_thread(conf->mddev->thread);
 }
 
@@ -2401,6 +2412,7 @@ void r5c_finish_stripe_write_out(struct r5conf *conf,
 	spin_unlock_irq(&conf->log->stripe_in_journal_lock);
 	sh->log_start = MaxSector;
 	atomic_dec(&conf->log->stripe_in_journal_count);
+	r5c_update_log_state(conf->log);
 }
 
 int