dm bio prison: switch to using a red black tree

Previously it was using a fixed sized hash table.  There are times
when very many concurrent cells are held (such as when processing a very
large discard).  When this happens the hash table performance becomes
very poor.

Signed-off-by: Joe Thornber <ejt@redhat.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>

1 files changed, 73 insertions, 99 deletions

diff --git a/drivers/md/dm-bio-prison.c b/drivers/md/dm-bio-prison.c
index f752d12081ff..90a56625245a 100644
--- a/drivers/md/dm-bio-prison.c
+++ b/drivers/md/dm-bio-prison.c
@@ -14,68 +14,38 @@
 
 /*----------------------------------------------------------------*/
 
-struct bucket {
-	spinlock_t lock;
-	struct hlist_head cells;
-};
+#define MIN_CELLS 1024
 
 struct dm_bio_prison {
+	spinlock_t lock;
 	mempool_t *cell_pool;
-
-	unsigned nr_buckets;
-	unsigned hash_mask;
-	struct bucket *buckets;
+	struct rb_root cells;
 };
 
-/*----------------------------------------------------------------*/
-
-static uint32_t calc_nr_buckets(unsigned nr_cells)
-{
-	uint32_t n = 128;
-
-	nr_cells /= 4;
-	nr_cells = min(nr_cells, 8192u);
-
-	while (n < nr_cells)
-		n <<= 1;
-
-	return n;
-}
-
 static struct kmem_cache *_cell_cache;
 
-static void init_bucket(struct bucket *b)
-{
-	spin_lock_init(&b->lock);
-	INIT_HLIST_HEAD(&b->cells);
-}
+/*----------------------------------------------------------------*/
 
 /*
  * @nr_cells should be the number of cells you want in use _concurrently_.
  * Don't confuse it with the number of distinct keys.
  */
-struct dm_bio_prison *dm_bio_prison_create(unsigned nr_cells)
+struct dm_bio_prison *dm_bio_prison_create(void)
 {
-	unsigned i;
-	uint32_t nr_buckets = calc_nr_buckets(nr_cells);
-	size_t len = sizeof(struct dm_bio_prison) +
-		(sizeof(struct bucket) * nr_buckets);
-	struct dm_bio_prison *prison = kmalloc(len, GFP_KERNEL);
+	struct dm_bio_prison *prison = kmalloc(sizeof(*prison), GFP_KERNEL);
 
 	if (!prison)
 		return NULL;
 
-	prison->cell_pool = mempool_create_slab_pool(nr_cells, _cell_cache);
+	spin_lock_init(&prison->lock);
+
+	prison->cell_pool = mempool_create_slab_pool(MIN_CELLS, _cell_cache);
 	if (!prison->cell_pool) {
 		kfree(prison);
 		return NULL;
 	}
 
-	prison->nr_buckets = nr_buckets;
-	prison->hash_mask = nr_buckets - 1;
-	prison->buckets = (struct bucket *) (prison + 1);
-	for (i = 0; i < nr_buckets; i++)
-		init_bucket(prison->buckets + i);
+	prison->cells = RB_ROOT;
 
 	return prison;
 }
@@ -101,68 +71,73 @@ void dm_bio_prison_free_cell(struct dm_bio_prison *prison,
 }
 EXPORT_SYMBOL_GPL(dm_bio_prison_free_cell);
 
-static uint32_t hash_key(struct dm_bio_prison *prison, struct dm_cell_key *key)
+static void __setup_new_cell(struct dm_cell_key *key,
+			     struct bio *holder,
+			     struct dm_bio_prison_cell *cell)
 {
-	const unsigned long BIG_PRIME = 4294967291UL;
-	uint64_t hash = key->block * BIG_PRIME;
-
-	return (uint32_t) (hash & prison->hash_mask);
+       memcpy(&cell->key, key, sizeof(cell->key));
+       cell->holder = holder;
+       bio_list_init(&cell->bios);
 }
 
-static int keys_equal(struct dm_cell_key *lhs, struct dm_cell_key *rhs)
+static int cmp_keys(struct dm_cell_key *lhs,
+		    struct dm_cell_key *rhs)
 {
-	       return (lhs->virtual == rhs->virtual) &&
-		       (lhs->dev == rhs->dev) &&
-		       (lhs->block == rhs->block);
-}
+	if (lhs->virtual < rhs->virtual)
+		return -1;
 
-static struct bucket *get_bucket(struct dm_bio_prison *prison,
-				 struct dm_cell_key *key)
-{
-	return prison->buckets + hash_key(prison, key);
-}
+	if (lhs->virtual > rhs->virtual)
+		return 1;
 
-static struct dm_bio_prison_cell *__search_bucket(struct bucket *b,
-						  struct dm_cell_key *key)
-{
-	struct dm_bio_prison_cell *cell;
+	if (lhs->dev < rhs->dev)
+		return -1;
 
-	hlist_for_each_entry(cell, &b->cells, list)
-		if (keys_equal(&cell->key, key))
-			return cell;
+	if (lhs->dev > rhs->dev)
+		return 1;
 
-	return NULL;
-}
+	if (lhs->block < rhs->block)
+		return -1;
 
-static void __setup_new_cell(struct bucket *b,
-			     struct dm_cell_key *key,
-			     struct bio *holder,
-			     struct dm_bio_prison_cell *cell)
-{
-	memcpy(&cell->key, key, sizeof(cell->key));
-	cell->holder = holder;
-	bio_list_init(&cell->bios);
-	hlist_add_head(&cell->list, &b->cells);
+	if (lhs->block > rhs->block)
+		return 1;
+
+	return 0;
 }
 
-static int __bio_detain(struct bucket *b,
+static int __bio_detain(struct dm_bio_prison *prison,
 			struct dm_cell_key *key,
 			struct bio *inmate,
 			struct dm_bio_prison_cell *cell_prealloc,
 			struct dm_bio_prison_cell **cell_result)
 {
-	struct dm_bio_prison_cell *cell;
-
-	cell = __search_bucket(b, key);
-	if (cell) {
-		if (inmate)
-			bio_list_add(&cell->bios, inmate);
-		*cell_result = cell;
-		return 1;
+	int r;
+	struct rb_node **new = &prison->cells.rb_node, *parent = NULL;
+
+	while (*new) {
+		struct dm_bio_prison_cell *cell =
+			container_of(*new, struct dm_bio_prison_cell, node);
+
+		r = cmp_keys(key, &cell->key);
+
+		parent = *new;
+		if (r < 0)
+			new = &((*new)->rb_left);
+		else if (r > 0)
+			new = &((*new)->rb_right);
+		else {
+			if (inmate)
+				bio_list_add(&cell->bios, inmate);
+			*cell_result = cell;
+			return 1;
+		}
 	}
 
-	__setup_new_cell(b, key, inmate, cell_prealloc);
+	__setup_new_cell(key, inmate, cell_prealloc);
 	*cell_result = cell_prealloc;
+
+	rb_link_node(&cell_prealloc->node, parent, new);
+	rb_insert_color(&cell_prealloc->node, &prison->cells);
+
 	return 0;
 }
 
@@ -174,11 +149,10 @@ static int bio_detain(struct dm_bio_prison *prison,
 {
 	int r;
 	unsigned long flags;
-	struct bucket *b = get_bucket(prison, key);
 
-	spin_lock_irqsave(&b->lock, flags);
-	r = __bio_detain(b, key, inmate, cell_prealloc, cell_result);
-	spin_unlock_irqrestore(&b->lock, flags);
+	spin_lock_irqsave(&prison->lock, flags);
+	r = __bio_detain(prison, key, inmate, cell_prealloc, cell_result);
+	spin_unlock_irqrestore(&prison->lock, flags);
 
 	return r;
 }
@@ -205,10 +179,11 @@ EXPORT_SYMBOL_GPL(dm_get_cell);
 /*
  * @inmates must have been initialised prior to this call
  */
-static void __cell_release(struct dm_bio_prison_cell *cell,
+static void __cell_release(struct dm_bio_prison *prison,
+			   struct dm_bio_prison_cell *cell,
 			   struct bio_list *inmates)
 {
-	hlist_del(&cell->list);
+	rb_erase(&cell->node, &prison->cells);
 
 	if (inmates) {
 		if (cell->holder)
@@ -222,21 +197,21 @@ void dm_cell_release(struct dm_bio_prison *prison,
 		     struct bio_list *bios)
 {
 	unsigned long flags;
-	struct bucket *b = get_bucket(prison, &cell->key);
 
-	spin_lock_irqsave(&b->lock, flags);
-	__cell_release(cell, bios);
-	spin_unlock_irqrestore(&b->lock, flags);
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release(prison, cell, bios);
+	spin_unlock_irqrestore(&prison->lock, flags);
 }
 EXPORT_SYMBOL_GPL(dm_cell_release);
 
 /*
  * Sometimes we don't want the holder, just the additional bios.
  */
-static void __cell_release_no_holder(struct dm_bio_prison_cell *cell,
+static void __cell_release_no_holder(struct dm_bio_prison *prison,
+				     struct dm_bio_prison_cell *cell,
 				     struct bio_list *inmates)
 {
-	hlist_del(&cell->list);
+	rb_erase(&cell->node, &prison->cells);
 	bio_list_merge(inmates, &cell->bios);
 }
 
@@ -245,11 +220,10 @@ void dm_cell_release_no_holder(struct dm_bio_prison *prison,
 			       struct bio_list *inmates)
 {
 	unsigned long flags;
-	struct bucket *b = get_bucket(prison, &cell->key);
 
-	spin_lock_irqsave(&b->lock, flags);
-	__cell_release_no_holder(cell, inmates);
-	spin_unlock_irqrestore(&b->lock, flags);
+	spin_lock_irqsave(&prison->lock, flags);
+	__cell_release_no_holder(prison, cell, inmates);
+	spin_unlock_irqrestore(&prison->lock, flags);
 }
 EXPORT_SYMBOL_GPL(dm_cell_release_no_holder);