- Update the dm-cache multiqueue policy to have a writeback_delay op…

…tion.

drivers/md/dm-cache-policy-mq.c

@@ -234,6 +234,7 @@ struct entry {
 	unsigned hit_count;
 	unsigned generation;
 	unsigned tick;
+	unsigned long dirty_writeback_after;
 };
 
 /*
@@ -393,6 +394,9 @@ struct mq_policy {
 	unsigned read_promote_adjustment;
 	unsigned write_promote_adjustment;
 
+	/* How long to wait before issuing a writeback */
+	unsigned writeback_delay;
+
 	/*
 	 * The hash table allows us to quickly find an entry by origin
 	 * block.  Both pre_cache and cache entries are in here.
@@ -406,6 +410,7 @@ struct mq_policy {
 #define DEFAULT_READ_PROMOTE_ADJUSTMENT 4
 #define DEFAULT_WRITE_PROMOTE_ADJUSTMENT 8
 #define DISCOURAGE_DEMOTING_DIRTY_THRESHOLD 128
+#define DEFAULT_WRITEBACK_DELAY 10
 
 /*----------------------------------------------------------------*/
 
@@ -969,6 +974,9 @@ static void __mq_set_clear_dirty(struct mq_policy *mq, dm_oblock_t oblock, bool
 
 	del(mq, e);
 	e->dirty = set;
+	if(set)
+		e->dirty_writeback_after = jiffies + (mq->writeback_delay * HZ);
+
 	push(mq, e);
 }
 
@@ -1090,9 +1098,12 @@ static int mq_remove_cblock(struct dm_cache_policy *p, dm_cblock_t cblock)
 static int __mq_writeback_work(struct mq_policy *mq, dm_oblock_t *oblock,
 			      dm_cblock_t *cblock)
 {
-	struct entry *e = pop(mq, &mq->cache_dirty);
+	struct entry *e = peek(&mq->cache_dirty);
+	if (!e || time_before(jiffies, e->dirty_writeback_after))
+		return -ENODATA;
 
-	if (!e)
+	e = pop(mq, &mq->cache_dirty);
+	if (unlikely(!e))
 		return -ENODATA;
 
 	*oblock = e->oblock;
@@ -1125,6 +1136,7 @@ static void __force_mapping(struct mq_policy *mq,
 		del(mq, e);
 		e->oblock = new_oblock;
 		e->dirty = true;
+		e->dirty_writeback_after = jiffies + (mq->writeback_delay * HZ);
 		push(mq, e);
 	}
 }
@@ -1185,6 +1197,9 @@ static int mq_set_config_value(struct dm_cache_policy *p,
 	else if (!strcasecmp(key, "write_promote_adjustment"))
 		mq->write_promote_adjustment = tmp;
 
+	else if (!strcasecmp(key, "writeback_delay"))
+		mq->writeback_delay = tmp;
+
 	else
 		return -EINVAL;
 
@@ -1196,16 +1211,18 @@ static int mq_emit_config_values(struct dm_cache_policy *p, char *result, unsign
 	ssize_t sz = 0;
 	struct mq_policy *mq = to_mq_policy(p);
 
-	DMEMIT("10 random_threshold %u "
+	DMEMIT("12 random_threshold %u "
 	       "sequential_threshold %u "
 	       "discard_promote_adjustment %u "
 	       "read_promote_adjustment %u "
-	       "write_promote_adjustment %u",
+	       "write_promote_adjustment %u "
+	       "writeback_delay %u",
 	       mq->tracker.thresholds[PATTERN_RANDOM],
 	       mq->tracker.thresholds[PATTERN_SEQUENTIAL],
 	       mq->discard_promote_adjustment,
 	       mq->read_promote_adjustment,
-	       mq->write_promote_adjustment);
+	       mq->write_promote_adjustment,
+	       mq->writeback_delay);
 
 	return 0;
 }
@@ -1260,6 +1277,7 @@ static struct dm_cache_policy *mq_create(dm_cblock_t cache_size,
 	mq->discard_promote_adjustment = DEFAULT_DISCARD_PROMOTE_ADJUSTMENT;
 	mq->read_promote_adjustment = DEFAULT_READ_PROMOTE_ADJUSTMENT;
 	mq->write_promote_adjustment = DEFAULT_WRITE_PROMOTE_ADJUSTMENT;
+	mq->writeback_delay = DEFAULT_WRITEBACK_DELAY;
 	mutex_init(&mq->lock);
 	spin_lock_init(&mq->tick_lock);