diff --git a/block/blk-mq-sysfs.c b/block/blk-mq-sysfs.c
index 8145b5b25b4b..99a60a829e69 100644
--- a/block/blk-mq-sysfs.c
+++ b/block/blk-mq-sysfs.c
@@ -208,6 +208,11 @@ static ssize_t blk_mq_hw_sysfs_tags_show(struct blk_mq_hw_ctx *hctx, char *page)
 	return blk_mq_tag_sysfs_show(hctx->tags, page);
 }
 
+static ssize_t blk_mq_hw_sysfs_active_show(struct blk_mq_hw_ctx *hctx, char *page)
+{
+	return sprintf(page, "%u\n", atomic_read(&hctx->nr_active));
+}
+
 static ssize_t blk_mq_hw_sysfs_cpus_show(struct blk_mq_hw_ctx *hctx, char *page)
 {
 	unsigned int i, first = 1;
@@ -267,6 +272,10 @@ static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_dispatched = {
 	.attr = {.name = "dispatched", .mode = S_IRUGO },
 	.show = blk_mq_hw_sysfs_dispatched_show,
 };
+static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_active = {
+	.attr = {.name = "active", .mode = S_IRUGO },
+	.show = blk_mq_hw_sysfs_active_show,
+};
 static struct blk_mq_hw_ctx_sysfs_entry blk_mq_hw_sysfs_pending = {
 	.attr = {.name = "pending", .mode = S_IRUGO },
 	.show = blk_mq_hw_sysfs_rq_list_show,
@@ -287,6 +296,7 @@ static struct attribute *default_hw_ctx_attrs[] = {
 	&blk_mq_hw_sysfs_pending.attr,
 	&blk_mq_hw_sysfs_tags.attr,
 	&blk_mq_hw_sysfs_cpus.attr,
+	&blk_mq_hw_sysfs_active.attr,
 	NULL,
 };
 
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 8d526a3e02f6..c80086c9c064 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -7,13 +7,12 @@
 #include "blk-mq.h"
 #include "blk-mq-tag.h"
 
-void blk_mq_wait_for_tags(struct blk_mq_tags *tags, struct blk_mq_hw_ctx *hctx,
-			  bool reserved)
+void blk_mq_wait_for_tags(struct blk_mq_hw_ctx *hctx, bool reserved)
 {
 	int tag, zero = 0;
 
-	tag = blk_mq_get_tag(tags, hctx, &zero, __GFP_WAIT, reserved);
-	blk_mq_put_tag(tags, tag, &zero);
+	tag = blk_mq_get_tag(hctx, &zero, __GFP_WAIT, reserved);
+	blk_mq_put_tag(hctx, tag, &zero);
 }
 
 static bool bt_has_free_tags(struct blk_mq_bitmap_tags *bt)
@@ -40,6 +39,84 @@ bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
 	return bt_has_free_tags(&tags->bitmap_tags);
 }
 
+static inline void bt_index_inc(unsigned int *index)
+{
+	*index = (*index + 1) & (BT_WAIT_QUEUES - 1);
+}
+
+/*
+ * If a previously inactive queue goes active, bump the active user count.
+ */
+bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
+{
+	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state) &&
+	    !test_and_set_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+		atomic_inc(&hctx->tags->active_queues);
+
+	return true;
+}
+
+/*
+ * If a previously busy queue goes inactive, potential waiters could now
+ * be allowed to queue. Wake them up and check.
+ */
+void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
+{
+	struct blk_mq_tags *tags = hctx->tags;
+	struct blk_mq_bitmap_tags *bt;
+	int i, wake_index;
+
+	if (!test_and_clear_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+		return;
+
+	atomic_dec(&tags->active_queues);
+
+	/*
+	 * Will only throttle depth on non-reserved tags
+	 */
+	bt = &tags->bitmap_tags;
+	wake_index = bt->wake_index;
+	for (i = 0; i < BT_WAIT_QUEUES; i++) {
+		struct bt_wait_state *bs = &bt->bs[wake_index];
+
+		if (waitqueue_active(&bs->wait))
+			wake_up(&bs->wait);
+
+		bt_index_inc(&wake_index);
+	}
+}
+
+/*
+ * For shared tag users, we track the number of currently active users
+ * and attempt to provide a fair share of the tag depth for each of them.
+ */
+static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
+				  struct blk_mq_bitmap_tags *bt)
+{
+	unsigned int depth, users;
+
+	if (!hctx || !(hctx->flags & BLK_MQ_F_TAG_SHARED))
+		return true;
+	if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
+		return true;
+
+	/*
+	 * Don't try dividing an ant
+	 */
+	if (bt->depth == 1)
+		return true;
+
+	users = atomic_read(&hctx->tags->active_queues);
+	if (!users)
+		return true;
+
+	/*
+	 * Allow at least some tags
+	 */
+	depth = max((bt->depth + users - 1) / users, 4U);
+	return atomic_read(&hctx->nr_active) < depth;
+}
+
 static int __bt_get_word(struct blk_mq_bitmap *bm, unsigned int last_tag)
 {
 	int tag, org_last_tag, end;
@@ -78,11 +155,15 @@ restart:
  * multiple users will tend to stick to different cachelines, at least
  * until the map is exhausted.
  */
-static int __bt_get(struct blk_mq_bitmap_tags *bt, unsigned int *tag_cache)
+static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
+		    unsigned int *tag_cache)
 {
 	unsigned int last_tag, org_last_tag;
 	int index, i, tag;
 
+	if (!hctx_may_queue(hctx, bt))
+		return -1;
+
 	last_tag = org_last_tag = *tag_cache;
 	index = TAG_TO_INDEX(bt, last_tag);
 
@@ -117,11 +198,6 @@ done:
 	return tag;
 }
 
-static inline void bt_index_inc(unsigned int *index)
-{
-	*index = (*index + 1) & (BT_WAIT_QUEUES - 1);
-}
-
 static struct bt_wait_state *bt_wait_ptr(struct blk_mq_bitmap_tags *bt,
 					 struct blk_mq_hw_ctx *hctx)
 {
@@ -142,7 +218,7 @@ static int bt_get(struct blk_mq_bitmap_tags *bt, struct blk_mq_hw_ctx *hctx,
 	DEFINE_WAIT(wait);
 	int tag;
 
-	tag = __bt_get(bt, last_tag);
+	tag = __bt_get(hctx, bt, last_tag);
 	if (tag != -1)
 		return tag;
 
@@ -156,7 +232,7 @@ static int bt_get(struct blk_mq_bitmap_tags *bt, struct blk_mq_hw_ctx *hctx,
 		was_empty = list_empty(&wait.task_list);
 		prepare_to_wait(&bs->wait, &wait, TASK_UNINTERRUPTIBLE);
 
-		tag = __bt_get(bt, last_tag);
+		tag = __bt_get(hctx, bt, last_tag);
 		if (tag != -1)
 			break;
 
@@ -200,14 +276,13 @@ static unsigned int __blk_mq_get_reserved_tag(struct blk_mq_tags *tags,
 	return tag;
 }
 
-unsigned int blk_mq_get_tag(struct blk_mq_tags *tags,
-			    struct blk_mq_hw_ctx *hctx, unsigned int *last_tag,
+unsigned int blk_mq_get_tag(struct blk_mq_hw_ctx *hctx, unsigned int *last_tag,
 			    gfp_t gfp, bool reserved)
 {
 	if (!reserved)
-		return __blk_mq_get_tag(tags, hctx, last_tag, gfp);
+		return __blk_mq_get_tag(hctx->tags, hctx, last_tag, gfp);
 
-	return __blk_mq_get_reserved_tag(tags, gfp);
+	return __blk_mq_get_reserved_tag(hctx->tags, gfp);
 }
 
 static struct bt_wait_state *bt_wake_ptr(struct blk_mq_bitmap_tags *bt)
@@ -265,9 +340,11 @@ static void __blk_mq_put_reserved_tag(struct blk_mq_tags *tags,
 	bt_clear_tag(&tags->breserved_tags, tag);
 }
 
-void blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag,
+void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag,
 		    unsigned int *last_tag)
 {
+	struct blk_mq_tags *tags = hctx->tags;
+
 	if (tag >= tags->nr_reserved_tags) {
 		const int real_tag = tag - tags->nr_reserved_tags;
 
@@ -465,6 +542,7 @@ ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page)
 	res = bt_unused_tags(&tags->breserved_tags);
 
 	page += sprintf(page, "nr_free=%u, nr_reserved=%u\n", free, res);
+	page += sprintf(page, "active_queues=%u\n", atomic_read(&tags->active_queues));
 
 	return page - orig_page;
 }
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 7aa9f0665489..0f5ec8b50ef3 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -38,6 +38,8 @@ struct blk_mq_tags {
 	unsigned int nr_tags;
 	unsigned int nr_reserved_tags;
 
+	atomic_t active_queues;
+
 	struct blk_mq_bitmap_tags bitmap_tags;
 	struct blk_mq_bitmap_tags breserved_tags;
 
@@ -49,9 +51,9 @@ struct blk_mq_tags {
 extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node);
 extern void blk_mq_free_tags(struct blk_mq_tags *tags);
 
-extern unsigned int blk_mq_get_tag(struct blk_mq_tags *tags, struct blk_mq_hw_ctx *hctx, unsigned int *last_tag, gfp_t gfp, bool reserved);
-extern void blk_mq_wait_for_tags(struct blk_mq_tags *tags, struct blk_mq_hw_ctx *hctx, bool reserved);
-extern void blk_mq_put_tag(struct blk_mq_tags *tags, unsigned int tag, unsigned int *last_tag);
+extern unsigned int blk_mq_get_tag(struct blk_mq_hw_ctx *hctx, unsigned int *last_tag, gfp_t gfp, bool reserved);
+extern void blk_mq_wait_for_tags(struct blk_mq_hw_ctx *hctx, bool reserved);
+extern void blk_mq_put_tag(struct blk_mq_hw_ctx *hctx, unsigned int tag, unsigned int *last_tag);
 extern void blk_mq_tag_busy_iter(struct blk_mq_tags *tags, void (*fn)(void *data, unsigned long *), void *data);
 extern bool blk_mq_has_free_tags(struct blk_mq_tags *tags);
 extern ssize_t blk_mq_tag_sysfs_show(struct blk_mq_tags *tags, char *page);
@@ -68,4 +70,23 @@ enum {
 	BLK_MQ_TAG_MAX		= BLK_MQ_TAG_FAIL - 1,
 };
 
+extern bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *);
+extern void __blk_mq_tag_idle(struct blk_mq_hw_ctx *);
+
+static inline bool blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
+{
+	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED))
+		return false;
+
+	return __blk_mq_tag_busy(hctx);
+}
+
+static inline void blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
+{
+	if (!(hctx->flags & BLK_MQ_F_TAG_SHARED))
+		return;
+
+	__blk_mq_tag_idle(hctx);
+}
+
 #endif
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 9f07a266f7ab..3c4f1fceef8e 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -80,9 +80,16 @@ static struct request *__blk_mq_alloc_request(struct blk_mq_hw_ctx *hctx,
 	struct request *rq;
 	unsigned int tag;
 
-	tag = blk_mq_get_tag(hctx->tags, hctx, &ctx->last_tag, gfp, reserved);
+	tag = blk_mq_get_tag(hctx, &ctx->last_tag, gfp, reserved);
 	if (tag != BLK_MQ_TAG_FAIL) {
 		rq = hctx->tags->rqs[tag];
+
+		rq->cmd_flags = 0;
+		if (blk_mq_tag_busy(hctx)) {
+			rq->cmd_flags = REQ_MQ_INFLIGHT;
+			atomic_inc(&hctx->nr_active);
+		}
+
 		rq->tag = tag;
 		return rq;
 	}
@@ -190,7 +197,7 @@ static void blk_mq_rq_ctx_init(struct request_queue *q, struct blk_mq_ctx *ctx,
 	/* csd/requeue_work/fifo_time is initialized before use */
 	rq->q = q;
 	rq->mq_ctx = ctx;
-	rq->cmd_flags = rw_flags;
+	rq->cmd_flags |= rw_flags;
 	rq->cmd_type = 0;
 	/* do not touch atomic flags, it needs atomic ops against the timer */
 	rq->cpu = -1;
@@ -262,7 +269,7 @@ static struct request *blk_mq_alloc_request_pinned(struct request_queue *q,
 			break;
 		}
 
-		blk_mq_wait_for_tags(hctx->tags, hctx, reserved);
+		blk_mq_wait_for_tags(hctx, reserved);
 	} while (1);
 
 	return rq;
@@ -303,8 +310,11 @@ static void __blk_mq_free_request(struct blk_mq_hw_ctx *hctx,
 	const int tag = rq->tag;
 	struct request_queue *q = rq->q;
 
+	if (rq->cmd_flags & REQ_MQ_INFLIGHT)
+		atomic_dec(&hctx->nr_active);
+
 	clear_bit(REQ_ATOM_STARTED, &rq->atomic_flags);
-	blk_mq_put_tag(hctx->tags, tag, &ctx->last_tag);
+	blk_mq_put_tag(hctx, tag, &ctx->last_tag);
 	blk_mq_queue_exit(q);
 }
 
@@ -571,8 +581,13 @@ static void blk_mq_rq_timer(unsigned long data)
 	queue_for_each_hw_ctx(q, hctx, i)
 		blk_mq_hw_ctx_check_timeout(hctx, &next, &next_set);
 
-	if (next_set)
-		mod_timer(&q->timeout, round_jiffies_up(next));
+	if (next_set) {
+		next = blk_rq_timeout(round_jiffies_up(next));
+		mod_timer(&q->timeout, next);
+	} else {
+		queue_for_each_hw_ctx(q, hctx, i)
+			blk_mq_tag_idle(hctx);
+	}
 }
 
 /*
@@ -1439,6 +1454,56 @@ static void blk_mq_map_swqueue(struct request_queue *q)
 	}
 }
 
+static void blk_mq_update_tag_set_depth(struct blk_mq_tag_set *set)
+{
+	struct blk_mq_hw_ctx *hctx;
+	struct request_queue *q;
+	bool shared;
+	int i;
+
+	if (set->tag_list.next == set->tag_list.prev)
+		shared = false;
+	else
+		shared = true;
+
+	list_for_each_entry(q, &set->tag_list, tag_set_list) {
+		blk_mq_freeze_queue(q);
+
+		queue_for_each_hw_ctx(q, hctx, i) {
+			if (shared)
+				hctx->flags |= BLK_MQ_F_TAG_SHARED;
+			else
+				hctx->flags &= ~BLK_MQ_F_TAG_SHARED;
+		}
+		blk_mq_unfreeze_queue(q);
+	}
+}
+
+static void blk_mq_del_queue_tag_set(struct request_queue *q)
+{
+	struct blk_mq_tag_set *set = q->tag_set;
+
+	blk_mq_freeze_queue(q);
+
+	mutex_lock(&set->tag_list_lock);
+	list_del_init(&q->tag_set_list);
+	blk_mq_update_tag_set_depth(set);
+	mutex_unlock(&set->tag_list_lock);
+
+	blk_mq_unfreeze_queue(q);
+}
+
+static void blk_mq_add_queue_tag_set(struct blk_mq_tag_set *set,
+				     struct request_queue *q)
+{
+	q->tag_set = set;
+
+	mutex_lock(&set->tag_list_lock);
+	list_add_tail(&q->tag_set_list, &set->tag_list);
+	blk_mq_update_tag_set_depth(set);
+	mutex_unlock(&set->tag_list_lock);
+}
+
 struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
 {
 	struct blk_mq_hw_ctx **hctxs;
@@ -1464,6 +1529,7 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
 		if (!zalloc_cpumask_var(&hctxs[i]->cpumask, GFP_KERNEL))
 			goto err_hctxs;
 
+		atomic_set(&hctxs[i]->nr_active, 0);
 		hctxs[i]->numa_node = NUMA_NO_NODE;
 		hctxs[i]->queue_num = i;
 	}
@@ -1516,6 +1582,8 @@ struct request_queue *blk_mq_init_queue(struct blk_mq_tag_set *set)
 	list_add_tail(&q->all_q_node, &all_q_list);
 	mutex_unlock(&all_q_mutex);
 
+	blk_mq_add_queue_tag_set(set, q);
+
 	return q;
 
 err_flush_rq:
@@ -1543,6 +1611,8 @@ void blk_mq_free_queue(struct request_queue *q)
 	struct blk_mq_hw_ctx *hctx;
 	int i;
 
+	blk_mq_del_queue_tag_set(q);
+
 	queue_for_each_hw_ctx(q, hctx, i) {
 		kfree(hctx->ctx_map);
 		kfree(hctx->ctxs);
@@ -1635,6 +1705,9 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 			goto out_unwind;
 	}
 
+	mutex_init(&set->tag_list_lock);
+	INIT_LIST_HEAD(&set->tag_list);
+
 	return 0;
 
 out_unwind:
diff --git a/block/blk-timeout.c b/block/blk-timeout.c
index 448745683d28..43e8b515806f 100644
--- a/block/blk-timeout.c
+++ b/block/blk-timeout.c
@@ -166,6 +166,17 @@ void blk_abort_request(struct request *req)
 }
 EXPORT_SYMBOL_GPL(blk_abort_request);
 
+unsigned long blk_rq_timeout(unsigned long timeout)
+{
+	unsigned long maxt;
+
+	maxt = round_jiffies_up(jiffies + BLK_MAX_TIMEOUT);
+	if (time_after(timeout, maxt))
+		timeout = maxt;
+
+	return timeout;
+}
+
 /**
  * blk_add_timer - Start timeout timer for a single request
  * @req:	request that is about to start running.
@@ -200,7 +211,7 @@ void blk_add_timer(struct request *req)
 	 * than an existing one, modify the timer. Round up to next nearest
 	 * second.
 	 */
-	expiry = round_jiffies_up(req->deadline);
+	expiry = blk_rq_timeout(round_jiffies_up(req->deadline));
 
 	if (!timer_pending(&q->timeout) ||
 	    time_before(expiry, q->timeout.expires)) {
diff --git a/block/blk.h b/block/blk.h
index 79be2cbce7fd..95cab70000e3 100644
--- a/block/blk.h
+++ b/block/blk.h
@@ -9,6 +9,9 @@
 /* Number of requests a "batching" process may submit */
 #define BLK_BATCH_REQ	32
 
+/* Max future timer expiry for timeouts */
+#define BLK_MAX_TIMEOUT		(5 * HZ)
+
 extern struct kmem_cache *blk_requestq_cachep;
 extern struct kmem_cache *request_cachep;
 extern struct kobj_type blk_queue_ktype;
@@ -37,6 +40,7 @@ bool __blk_end_bidi_request(struct request *rq, int error,
 void blk_rq_timed_out_timer(unsigned long data);
 void blk_rq_check_expired(struct request *rq, unsigned long *next_timeout,
 			  unsigned int *next_set);
+unsigned long blk_rq_timeout(unsigned long timeout);
 void blk_add_timer(struct request *req);
 void blk_delete_timer(struct request *);
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f83d15f6e1c1..379f88d5c44d 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -48,6 +48,8 @@ struct blk_mq_hw_ctx {
 	unsigned int		numa_node;
 	unsigned int		cmd_size;	/* per-request extra data */
 
+	atomic_t		nr_active;
+
 	struct blk_mq_cpu_notifier	cpu_notifier;
 	struct kobject		kobj;
 };
@@ -64,6 +66,9 @@ struct blk_mq_tag_set {
 	void			*driver_data;
 
 	struct blk_mq_tags	**tags;
+
+	struct mutex		tag_list_lock;
+	struct list_head	tag_list;
 };
 
 typedef int (queue_rq_fn)(struct blk_mq_hw_ctx *, struct request *);
@@ -126,8 +131,10 @@ enum {
 
 	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
 	BLK_MQ_F_SHOULD_SORT	= 1 << 1,
+	BLK_MQ_F_TAG_SHARED	= 1 << 2,
 
 	BLK_MQ_S_STOPPED	= 0,
+	BLK_MQ_S_TAG_ACTIVE	= 1,
 
 	BLK_MQ_MAX_DEPTH	= 2048,
 
diff --git a/include/linux/blk_types.h b/include/linux/blk_types.h
index aa0eaa2d0bd8..d8e4cea23a25 100644
--- a/include/linux/blk_types.h
+++ b/include/linux/blk_types.h
@@ -190,6 +190,7 @@ enum rq_flag_bits {
 	__REQ_PM,		/* runtime pm request */
 	__REQ_END,		/* last of chain of requests */
 	__REQ_HASHED,		/* on IO scheduler merge hash */
+	__REQ_MQ_INFLIGHT,	/* track inflight for MQ */
 	__REQ_NR_BITS,		/* stops here */
 };
 
@@ -243,5 +244,6 @@ enum rq_flag_bits {
 #define REQ_PM			(1ULL << __REQ_PM)
 #define REQ_END			(1ULL << __REQ_END)
 #define REQ_HASHED		(1ULL << __REQ_HASHED)
+#define REQ_MQ_INFLIGHT		(1ULL << __REQ_MQ_INFLIGHT)
 
 #endif /* __LINUX_BLK_TYPES_H */
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 94b27210641b..6bc011a09e82 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -481,6 +481,9 @@ struct request_queue {
 	wait_queue_head_t	mq_freeze_wq;
 	struct percpu_counter	mq_usage_counter;
 	struct list_head	all_q_node;
+
+	struct blk_mq_tag_set	*tag_set;
+	struct list_head	tag_set_list;
 };
 
 #define QUEUE_FLAG_QUEUED	1	/* uses generic tag queueing */