[04/11] blk-mq: Facilitate a shared sbitmap per tagset

Message ID 20191202153914.84722-5-hare@suse.de
State New
Headers show
Series
  • [01/11] blk-mq: Remove some unused function arguments
Related show

Commit Message

Hannes Reinecke Dec. 2, 2019, 3:39 p.m.
From: John Garry <john.garry@huawei.com>


Some SCSI HBAs (such as HPSA, megaraid, mpt3sas, hisi_sas_v3 ..) support
multiple reply queues with single hostwide tags.

In addition, these drivers want to use interrupt assignment in
pci_alloc_irq_vectors(PCI_IRQ_AFFINITY). However, as discussed in [0],
CPU hotplug may cause in-flight IO completion to not be serviced when an
interrupt is shutdown.

To solve that problem, Ming's patchset to drain hctx's should ensure no
IOs are missed in-flight [1].

However, to take advantage of that patchset, we need to map the HBA HW
queues to blk mq hctx's; to do that, we need to expose the HBA HW queues.

In making that transition, the per-SCSI command request tags are no
longer unique per Scsi host - they are just unique per hctx. As such, the
HBA LLDD would have to generate this tag internally, which has a certain
performance overhead.

However another problem is that blk mq assumes the host may accept
(Scsi_host.can_queue * #hw queue) commands. In [2], we removed the Scsi
host busy counter, which would stop the LLDD being sent more than
.can_queue commands; however, we should still ensure that the block layer
does not issue more than .can_queue commands to the Scsi host.

To solve this problem, introduce a shared sbitmap per blk_mq_tag_set,
which may be requested at init time.

New flag BLK_MQ_F_TAG_HCTX_SHARED should be set when requesting the
tagset to indicate whether the shared sbitmap should be used.

Even when BLK_MQ_F_TAG_HCTX_SHARED is set, we still allocate a full set of
tags and requests per hctx; the reason for this is that if we only allocate
tags and requests for a single hctx - like hctx0 - we may break block
drivers which expect a request be associated with a specific hctx, i.e.
not hctx0.

This is based on work originally from Ming Lei in [3] and from Bart's
suggestion in [4].

[0] https://lore.kernel.org/linux-block/alpine.DEB.2.21.1904051331270.1802@nanos.tec.linutronix.de/
[1] https://lore.kernel.org/linux-block/20191014015043.25029-1-ming.lei@redhat.com/
[2] https://lore.kernel.org/linux-scsi/20191025065855.6309-1-ming.lei@redhat.com/
[3] https://lore.kernel.org/linux-block/20190531022801.10003-1-ming.lei@redhat.com/
[4] https://lore.kernel.org/linux-block/ff77beff-5fd9-9f05-12b6-826922bace1f@huawei.com/T/#m3db0a602f095cbcbff27e9c884d6b4ae826144be

Signed-off-by: John Garry <john.garry@huawei.com>

Signed-off-by: Hannes Reinecke <hare@suse.de>

---
 block/bfq-iosched.c    |   4 +-
 block/blk-mq-debugfs.c |  10 ++---
 block/blk-mq-sched.c   |  14 ++++++
 block/blk-mq-tag.c     | 114 +++++++++++++++++++++++++++++++++++++++----------
 block/blk-mq-tag.h     |  17 ++++++--
 block/blk-mq.c         |  67 ++++++++++++++++++++++++++---
 block/blk-mq.h         |   5 +++
 block/kyber-iosched.c  |   4 +-
 include/linux/blk-mq.h |   9 ++++
 9 files changed, 204 insertions(+), 40 deletions(-)

-- 
2.16.4

Comments

John Garry Dec. 3, 2019, 2:54 p.m. | #1
>   

> @@ -483,8 +483,8 @@ static int hctx_tags_bitmap_show(void *data, struct seq_file *m)

>   	res = mutex_lock_interruptible(&q->sysfs_lock);

>   	if (res)

>   		goto out;

> -	if (hctx->tags)

> -		sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);

> +	if (hctx->tags) /* We should just iterate the relevant bits for this hctx FIXME */


Bart's solution to this problem seemed ok, if he doesn't mind us 
borrowing his idea:

https://lore.kernel.org/linux-block/5183ab13-0c81-95f0-95ba-40318569c6c6@huawei.com/T/#m24394fe70b1ea79a154dfd9620f5e553c3e7e7da

See hctx_tags_bitmap_show().

It might be also reasonable to put that in another follow on patch, as 
there would be no enablers of the "shared" bitmap until later patches.

> +		sbitmap_bitmap_show(&hctx->tags->bitmap_tags->sb, m);

>   	mutex_unlock(&q->sysfs_lock);

>   

>   out:

> @@ -518,7 +518,7 @@ static int hctx_sched_tags_bitmap_show(void *data, struct seq_file *m)

>   	if (res)

>   		goto out;

>   	if (hctx->sched_tags)

> -		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags.sb, m);

> +		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags->sb, m);

>   	mutex_unlock(&q->sysfs_lock);

>   

>   out:

> diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c

> index ca22afd47b3d..1855f8f5edd4 100644

> --- a/block/blk-mq-sched.c

> +++ b/block/blk-mq-sched.c

> @@ -492,6 +492,7 @@ static void blk_mq_sched_tags_teardown(struct request_queue *q)

>   

>   int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)

>   {

> +	struct blk_mq_tag_set *tag_set = q->tag_set;

>   	struct blk_mq_hw_ctx *hctx;

>   	struct elevator_queue *eq;

>   	unsigned int i;

> @@ -537,6 +538,19 @@ int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)

>   		blk_mq_debugfs_register_sched_hctx(q, hctx);

>   	}

>   

> +	if (blk_mq_is_sbitmap_shared(tag_set)) {

> +		if (!blk_mq_init_sched_shared_sbitmap(tag_set, q->nr_requests)) {

> +			ret = -ENOMEM;

> +			goto err;

> +		}

> +		queue_for_each_hw_ctx(q, hctx, i) {

> +			struct blk_mq_tags *tags = hctx->sched_tags;

> +

> +			tags->bitmap_tags = &tag_set->__sched_bitmap_tags;

> +			tags->breserved_tags = &tag_set->__sched_breserved_tags;

> +		}

> +	}

> +

>   	return 0;

>   

>   err:

> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c

> index f5009587e1b5..2e714123e846 100644

> --- a/block/blk-mq-tag.c

> +++ b/block/blk-mq-tag.c

> @@ -20,7 +20,7 @@ bool blk_mq_has_free_tags(struct blk_mq_tags *tags)

>   	if (!tags)

>   		return true;

>   

> -	return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);

> +	return sbitmap_any_bit_clear(&tags->bitmap_tags->sb);

>   }

>   

>   /*

> @@ -43,9 +43,9 @@ bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)

>    */

>   void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)

>   {

> -	sbitmap_queue_wake_all(&tags->bitmap_tags);

> +	sbitmap_queue_wake_all(tags->bitmap_tags);

>   	if (include_reserve)

> -		sbitmap_queue_wake_all(&tags->breserved_tags);

> +		sbitmap_queue_wake_all(tags->breserved_tags);

>   }

>   

>   /*

> @@ -121,10 +121,10 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)

>   			WARN_ON_ONCE(1);

>   			return BLK_MQ_TAG_FAIL;

>   		}

> -		bt = &tags->breserved_tags;

> +		bt = tags->breserved_tags;


We could put all of this in an earlier patch (as you had in v4, modulo 
dynamic memory part), which would be easier to review and get accepted.

>   		tag_offset = 0;

>   	} else {

> -		bt = &tags->bitmap_tags;

> +		bt = tags->bitmap_tags;

>   		tag_offset = tags->nr_reserved_tags;

>   	}



[...]

>   	if (!set)

> @@ -3160,6 +3179,7 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)

>   			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,

>   							false);

>   		} else {

> +			sched_tags = true;

>   			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,

>   							nr, true);

>   		}

> @@ -3169,8 +3189,43 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)

>   			q->elevator->type->ops.depth_updated(hctx);

>   	}

>   

> -	if (!ret)

> +	/*

> +	 * if ret is 0, all queues should have been updated to the same depth

> +	 * if not, then maybe some have been updated - yuk, need to handle this for shared sbitmap...

> +	 * if some are updated, we should probably roll back the change altogether. FIXME

> +	 */


If you don't have a shared sched bitmap - which I didn't think we needed 
- then all we need is a simple sbitmap_queue_resize(&tagset->__bitmap_tags)

Otherwise it's horrible to resize shared sched bitmaps...

> +	if (!ret) {

> +		if (blk_mq_is_sbitmap_shared(set)) {

> +			if (sched_tags) {

> +				blk_mq_exit_shared_sched_sbitmap(set);

> +				if (!blk_mq_init_sched_shared_sbitmap(set, nr))

> +					return -ENOMEM; /* fixup error handling */

> +

> +				queue_for_each_hw_ctx(q, hctx, i) {

> +					hctx->sched_tags->bitmap_tags =

> +						&set->__sched_bitmap_tags;

> +					hctx->sched_tags->breserved_tags =

> +						&set->__sched_breserved_tags;

> +				}

> +			} else {

> +				blk_mq_exit_shared_sbitmap(set);

> +				if (!blk_mq_init_shared_sbitmap(set))

> +					return -ENOMEM; /* fixup error handling */

> +

> +				queue_for_each_hw_ctx(q, hctx, i) {

> +					hctx->tags->bitmap_tags =

> +						&set->__bitmap_tags;

> +					hctx->tags->breserved_tags =

> +						&set->__breserved_tags;

> +				}

> +			}

> +		}

>   		q->nr_requests = nr;

> +	}

> +	/*

> +	 * if ret != 0, q->nr_requests would not be updated, yet the depth

> +	 * for some hctx may have changed - is that right?

> +	 */

>   

>   	blk_mq_unquiesce_queue(q);

>   	blk_mq_unfreeze_queue(q);

> diff --git a/block/blk-mq.h b/block/blk-mq.h

> index 78d38b5f2793..4c1ea206d3f4 100644

> --- a/block/blk-mq.h

> +++ b/block/blk-mq.h

> @@ -166,6 +166,11 @@ struct blk_mq_alloc_data {

>   	struct blk_mq_hw_ctx *hctx;

>   };

>   

> +static inline bool blk_mq_is_sbitmap_shared(struct blk_mq_tag_set *tag_set)

> +{

> +	return !!(tag_set->flags & BLK_MQ_F_TAG_HCTX_SHARED);


Bart already gave some comments on this

> +}

> +

>   static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data *data)

>   {

>   	if (data->flags & BLK_MQ_REQ_INTERNAL)

> diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c

> index 34dcea0ef637..a7a537501d70 100644

> --- a/block/kyber-iosched.c

> +++ b/block/kyber-iosched.c

> @@ -359,7 +359,7 @@ static unsigned int kyber_sched_tags_shift(struct request_queue *q)

>   	 * All of the hardware queues have the same depth, so we can just grab

>   	 * the shift of the first one.

>   	 */

> -	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;

> +	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;

>   }

>   

>   static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)

> @@ -502,7 +502,7 @@ static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)

>   	khd->batching = 0;

>   

>   	hctx->sched_data = khd;

> -	sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,

> +	sbitmap_queue_min_shallow_depth(hctx->sched_tags->bitmap_tags,

>   					kqd->async_depth);

>   

>   	return 0;

> diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h

> index 147185394a25..10c9ed3dbe80 100644

> --- a/include/linux/blk-mq.h

> +++ b/include/linux/blk-mq.h

> @@ -109,6 +109,12 @@ struct blk_mq_tag_set {

>   	unsigned int		flags;		/* BLK_MQ_F_* */

>   	void			*driver_data;

>   

> +	struct sbitmap_queue	__bitmap_tags;

> +	struct sbitmap_queue	__breserved_tags;

> +

> +	struct sbitmap_queue	__sched_bitmap_tags;

> +	struct sbitmap_queue	__sched_breserved_tags;

> +

>   	struct blk_mq_tags	**tags;

>   

>   	struct mutex		tag_list_lock;

> @@ -226,6 +232,9 @@ struct blk_mq_ops {

>   enum {

>   	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,

>   	BLK_MQ_F_TAG_QUEUE_SHARED	= 1 << 1,

> +	BLK_MQ_F_TAG_HCTX_SHARED	= 1 << 2,

> +	BLK_MQ_F_TAG_BITMAP_ALLOCATED	= 1 << 3,

> +	BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED = 1 << 4,

>   	BLK_MQ_F_BLOCKING	= 1 << 5,

>   	BLK_MQ_F_NO_SCHED	= 1 << 6,

>   	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,

>
Hannes Reinecke Dec. 3, 2019, 3:02 p.m. | #2
On 12/3/19 3:54 PM, John Garry wrote:
>>   @@ -483,8 +483,8 @@ static int hctx_tags_bitmap_show(void *data,

>> struct seq_file *m)

>>       res = mutex_lock_interruptible(&q->sysfs_lock);

>>       if (res)

>>           goto out;

>> -    if (hctx->tags)

>> -        sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);

>> +    if (hctx->tags) /* We should just iterate the relevant bits for

>> this hctx FIXME */

> 

> Bart's solution to this problem seemed ok, if he doesn't mind us

> borrowing his idea:

> 

> https://lore.kernel.org/linux-block/5183ab13-0c81-95f0-95ba-40318569c6c6@huawei.com/T/#m24394fe70b1ea79a154dfd9620f5e553c3e7e7da

> 

> 

> See hctx_tags_bitmap_show().

> 

> It might be also reasonable to put that in another follow on patch, as

> there would be no enablers of the "shared" bitmap until later patches.

> 

Yeah, that was my plan, too.
But then I'd rather wait for feedback on the general approach here;
no point is wasting perfectly good bits if no-one's wanting them ...

[ .. ]
>> @@ -121,10 +121,10 @@ unsigned int blk_mq_get_tag(struct

>> blk_mq_alloc_data *data)

>>               WARN_ON_ONCE(1);

>>               return BLK_MQ_TAG_FAIL;

>>           }

>> -        bt = &tags->breserved_tags;

>> +        bt = tags->breserved_tags;

> 

> We could put all of this in an earlier patch (as you had in v4, modulo

> dynamic memory part), which would be easier to review and get accepted.

> 

Yeah, but I felt it a bit odd, just having pointers to an existing
structure element.
But yes, will be doing for the next round.

>>           tag_offset = 0;

>>       } else {

>> -        bt = &tags->bitmap_tags;

>> +        bt = tags->bitmap_tags;

>>           tag_offset = tags->nr_reserved_tags;

>>       }

> 

> 

> [...]

> 

>>       if (!set)

>> @@ -3160,6 +3179,7 @@ int blk_mq_update_nr_requests(struct

>> request_queue *q, unsigned int nr)

>>               ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,

>>                               false);

>>           } else {

>> +            sched_tags = true;

>>               ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,

>>                               nr, true);

>>           }

>> @@ -3169,8 +3189,43 @@ int blk_mq_update_nr_requests(struct

>> request_queue *q, unsigned int nr)

>>               q->elevator->type->ops.depth_updated(hctx);

>>       }

>>   -    if (!ret)

>> +    /*

>> +     * if ret is 0, all queues should have been updated to the same

>> depth

>> +     * if not, then maybe some have been updated - yuk, need to

>> handle this for shared sbitmap...

>> +     * if some are updated, we should probably roll back the change

>> altogether. FIXME

>> +     */

> 

> If you don't have a shared sched bitmap - which I didn't think we needed

> - then all we need is a simple sbitmap_queue_resize(&tagset->__bitmap_tags)

> 

> Otherwise it's horrible to resize shared sched bitmaps...

> 

Resizing shared sched bitmaps is done in patch 6/11.
General idea is to move the scheduler bitmap into the request queue
(well, actually the elevator), as this gives us a per-request_queue
bitmap. Which is actually what we want here, as the scheduler will need
to look at all requests, hence needing to access to the same bitmap.
And it also gives us an easy way of resizing the sched tag bitmap, as
then we can resize the bitmap on a per-queue basis, and leave the
underlying tagset bitmap untouched.

[ .. ]
>> diff --git a/block/blk-mq.h b/block/blk-mq.h

>> index 78d38b5f2793..4c1ea206d3f4 100644

>> --- a/block/blk-mq.h

>> +++ b/block/blk-mq.h

>> @@ -166,6 +166,11 @@ struct blk_mq_alloc_data {

>>       struct blk_mq_hw_ctx *hctx;

>>   };

>>   +static inline bool blk_mq_is_sbitmap_shared(struct blk_mq_tag_set

>> *tag_set)

>> +{

>> +    return !!(tag_set->flags & BLK_MQ_F_TAG_HCTX_SHARED);

> 

> Bart already gave some comments on this

> 

Ah. Missed that one. Will be including in the next round.

Thanks for the review!

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      Teamlead Storage & Networking
hare@suse.de			                  +49 911 74053 688
SUSE Software Solutions Germany GmbH, Maxfeldstr. 5, 90409 Nürnberg
HRB 36809 (AG Nürnberg), GF: Felix Imendörffer
Bart Van Assche Dec. 3, 2019, 4:38 p.m. | #3
On 12/3/19 6:54 AM, John Garry wrote:
>> @@ -483,8 +483,8 @@ static int hctx_tags_bitmap_show(void *data, 

>> struct seq_file *m)

>>       res = mutex_lock_interruptible(&q->sysfs_lock);

>>       if (res)

>>           goto out;

>> -    if (hctx->tags)

>> -        sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);

>> +    if (hctx->tags) /* We should just iterate the relevant bits for 

>> this hctx FIXME */

> 

> Bart's solution to this problem seemed ok, if he doesn't mind us 

> borrowing his idea:

> 

> https://lore.kernel.org/linux-block/5183ab13-0c81-95f0-95ba-40318569c6c6@huawei.com/T/#m24394fe70b1ea79a154dfd9620f5e553c3e7e7da 

>  

> See hctx_tags_bitmap_show().


Hi John,

Sure, borrowing that code is fine with me.

Bart.
John Garry Dec. 4, 2019, 10:24 a.m. | #4
On 03/12/2019 15:02, Hannes Reinecke wrote:
>>> +     */

>> If you don't have a shared sched bitmap - which I didn't think we needed

>> - then all we need is a simple sbitmap_queue_resize(&tagset->__bitmap_tags)

>>

>> Otherwise it's horrible to resize shared sched bitmaps...

>>

> Resizing shared sched bitmaps is done in patch 6/11.

> General idea is to move the scheduler bitmap into the request queue

> (well, actually the elevator), as this gives us a per-request_queue

> bitmap. Which is actually what we want here, as the scheduler will need

> to look at all requests, hence needing to access to the same bitmap.

> And it also gives us an easy way of resizing the sched tag bitmap, as

> then we can resize the bitmap on a per-queue basis, and leave the

> underlying tagset bitmap untouched.


OK, but I am just concerned if that is really required in this series 
and whether it is just another obstacle to getting it accepted.

Thanks,
John

> 

> [ .. ]

>>> diff --git a/block/blk-mq.h b/block/blk-mq.h

>>> index 78d38b5f2793..4c1ea206d3f4 100644

>>> --- a/block/blk-mq.h

>>> +++ b/block/blk-mq.h

Patch

diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c
index 0319d6339822..ca89d0c34994 100644
--- a/block/bfq-iosched.c
+++ b/block/bfq-iosched.c
@@ -6327,8 +6327,8 @@  static void bfq_depth_updated(struct blk_mq_hw_ctx *hctx)
 	struct blk_mq_tags *tags = hctx->sched_tags;
 	unsigned int min_shallow;
 
-	min_shallow = bfq_update_depths(bfqd, &tags->bitmap_tags);
-	sbitmap_queue_min_shallow_depth(&tags->bitmap_tags, min_shallow);
+	min_shallow = bfq_update_depths(bfqd, tags->bitmap_tags);
+	sbitmap_queue_min_shallow_depth(tags->bitmap_tags, min_shallow);
 }
 
 static int bfq_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int index)
diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index 33a40ae1d60f..46f57dbed890 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -449,11 +449,11 @@  static void blk_mq_debugfs_tags_show(struct seq_file *m,
 		   atomic_read(&tags->active_queues));
 
 	seq_puts(m, "\nbitmap_tags:\n");
-	sbitmap_queue_show(&tags->bitmap_tags, m);
+	sbitmap_queue_show(tags->bitmap_tags, m);
 
 	if (tags->nr_reserved_tags) {
 		seq_puts(m, "\nbreserved_tags:\n");
-		sbitmap_queue_show(&tags->breserved_tags, m);
+		sbitmap_queue_show(tags->breserved_tags, m);
 	}
 }
 
@@ -483,8 +483,8 @@  static int hctx_tags_bitmap_show(void *data, struct seq_file *m)
 	res = mutex_lock_interruptible(&q->sysfs_lock);
 	if (res)
 		goto out;
-	if (hctx->tags)
-		sbitmap_bitmap_show(&hctx->tags->bitmap_tags.sb, m);
+	if (hctx->tags) /* We should just iterate the relevant bits for this hctx FIXME */
+		sbitmap_bitmap_show(&hctx->tags->bitmap_tags->sb, m);
 	mutex_unlock(&q->sysfs_lock);
 
 out:
@@ -518,7 +518,7 @@  static int hctx_sched_tags_bitmap_show(void *data, struct seq_file *m)
 	if (res)
 		goto out;
 	if (hctx->sched_tags)
-		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags.sb, m);
+		sbitmap_bitmap_show(&hctx->sched_tags->bitmap_tags->sb, m);
 	mutex_unlock(&q->sysfs_lock);
 
 out:
diff --git a/block/blk-mq-sched.c b/block/blk-mq-sched.c
index ca22afd47b3d..1855f8f5edd4 100644
--- a/block/blk-mq-sched.c
+++ b/block/blk-mq-sched.c
@@ -492,6 +492,7 @@  static void blk_mq_sched_tags_teardown(struct request_queue *q)
 
 int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 {
+	struct blk_mq_tag_set *tag_set = q->tag_set;
 	struct blk_mq_hw_ctx *hctx;
 	struct elevator_queue *eq;
 	unsigned int i;
@@ -537,6 +538,19 @@  int blk_mq_init_sched(struct request_queue *q, struct elevator_type *e)
 		blk_mq_debugfs_register_sched_hctx(q, hctx);
 	}
 
+	if (blk_mq_is_sbitmap_shared(tag_set)) {
+		if (!blk_mq_init_sched_shared_sbitmap(tag_set, q->nr_requests)) {
+			ret = -ENOMEM;
+			goto err;
+		}
+		queue_for_each_hw_ctx(q, hctx, i) {
+			struct blk_mq_tags *tags = hctx->sched_tags;
+
+			tags->bitmap_tags = &tag_set->__sched_bitmap_tags;
+			tags->breserved_tags = &tag_set->__sched_breserved_tags;
+		}
+	}
+
 	return 0;
 
 err:
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index f5009587e1b5..2e714123e846 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -20,7 +20,7 @@  bool blk_mq_has_free_tags(struct blk_mq_tags *tags)
 	if (!tags)
 		return true;
 
-	return sbitmap_any_bit_clear(&tags->bitmap_tags.sb);
+	return sbitmap_any_bit_clear(&tags->bitmap_tags->sb);
 }
 
 /*
@@ -43,9 +43,9 @@  bool __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
  */
 void blk_mq_tag_wakeup_all(struct blk_mq_tags *tags, bool include_reserve)
 {
-	sbitmap_queue_wake_all(&tags->bitmap_tags);
+	sbitmap_queue_wake_all(tags->bitmap_tags);
 	if (include_reserve)
-		sbitmap_queue_wake_all(&tags->breserved_tags);
+		sbitmap_queue_wake_all(tags->breserved_tags);
 }
 
 /*
@@ -121,10 +121,10 @@  unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 			WARN_ON_ONCE(1);
 			return BLK_MQ_TAG_FAIL;
 		}
-		bt = &tags->breserved_tags;
+		bt = tags->breserved_tags;
 		tag_offset = 0;
 	} else {
-		bt = &tags->bitmap_tags;
+		bt = tags->bitmap_tags;
 		tag_offset = tags->nr_reserved_tags;
 	}
 
@@ -170,9 +170,9 @@  unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data)
 						data->ctx);
 		tags = blk_mq_tags_from_data(data);
 		if (data->flags & BLK_MQ_REQ_RESERVED)
-			bt = &tags->breserved_tags;
+			bt = tags->breserved_tags;
 		else
-			bt = &tags->bitmap_tags;
+			bt = tags->bitmap_tags;
 
 		/*
 		 * If destination hw queue is changed, fake wake up on
@@ -198,10 +198,10 @@  void blk_mq_put_tag(struct blk_mq_tags *tags, struct blk_mq_ctx *ctx,
 		const int real_tag = tag - tags->nr_reserved_tags;
 
 		BUG_ON(real_tag >= tags->nr_tags);
-		sbitmap_queue_clear(&tags->bitmap_tags, real_tag, ctx->cpu);
+		sbitmap_queue_clear(tags->bitmap_tags, real_tag, ctx->cpu);
 	} else {
 		BUG_ON(tag >= tags->nr_reserved_tags);
-		sbitmap_queue_clear(&tags->breserved_tags, tag, ctx->cpu);
+		sbitmap_queue_clear(tags->breserved_tags, tag, ctx->cpu);
 	}
 }
 
@@ -228,7 +228,7 @@  static bool bt_iter(struct sbitmap *bitmap, unsigned int bitnr, void *data)
 	 * We can hit rq == NULL here, because the tagging functions
 	 * test and set the bit before assigning ->rqs[].
 	 */
-	if (rq && rq->q == hctx->queue)
+	if (rq && rq->q == hctx->queue && rq->mq_hctx == hctx)
 		return iter_data->fn(hctx, rq, iter_data->data, reserved);
 	return true;
 }
@@ -329,8 +329,8 @@  static void blk_mq_all_tag_busy_iter(struct blk_mq_tags *tags,
 		busy_tag_iter_fn *fn, void *priv)
 {
 	if (tags->nr_reserved_tags)
-		bt_tags_for_each(tags, &tags->breserved_tags, fn, priv, true);
-	bt_tags_for_each(tags, &tags->bitmap_tags, fn, priv, false);
+		bt_tags_for_each(tags, tags->breserved_tags, fn, priv, true);
+	bt_tags_for_each(tags, tags->bitmap_tags, fn, priv, false);
 }
 
 /**
@@ -427,8 +427,8 @@  void blk_mq_queue_tag_busy_iter(struct request_queue *q, busy_iter_fn *fn,
 			continue;
 
 		if (tags->nr_reserved_tags)
-			bt_for_each(hctx, &tags->breserved_tags, fn, priv, true);
-		bt_for_each(hctx, &tags->bitmap_tags, fn, priv, false);
+			bt_for_each(hctx, tags->breserved_tags, fn, priv, true);
+		bt_for_each(hctx, tags->bitmap_tags, fn, priv, false);
 	}
 	blk_queue_exit(q);
 }
@@ -446,19 +446,85 @@  static int blk_mq_init_bitmap_tags(struct blk_mq_tags *tags,
 	unsigned int depth = tags->nr_tags - tags->nr_reserved_tags;
 	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
 
-	if (bt_alloc(&tags->bitmap_tags, depth, round_robin, node))
+	if (bt_alloc(&tags->__bitmap_tags, depth, round_robin, node))
 		return -ENOMEM;
-	if (bt_alloc(&tags->breserved_tags, tags->nr_reserved_tags, round_robin,
-		     node))
+	if (bt_alloc(&tags->__breserved_tags, tags->nr_reserved_tags,
+		     round_robin, node))
 		goto free_bitmap_tags;
 
+	tags->bitmap_tags = &tags->__bitmap_tags;
+	tags->breserved_tags = &tags->__breserved_tags;
+
 	return 0;
 free_bitmap_tags:
-	sbitmap_queue_free(&tags->bitmap_tags);
+	sbitmap_queue_free(&tags->__bitmap_tags);
 	return -ENOMEM;
 }
 
-struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
+bool blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *tag_set)
+{
+	unsigned int depth = tag_set->queue_depth -tag_set->reserved_tags;
+	int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(tag_set->flags);
+	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
+	int node = tag_set->numa_node;
+
+	if (tag_set->flags & BLK_MQ_F_TAG_BITMAP_ALLOCATED)
+		return false;
+	if (bt_alloc(&tag_set->__bitmap_tags, depth, round_robin, node))
+		return false;
+	if (bt_alloc(&tag_set->__breserved_tags, tag_set->reserved_tags, round_robin,
+			 node))
+		goto free_bitmap_tags;
+	tag_set->flags |= BLK_MQ_F_TAG_BITMAP_ALLOCATED;
+	return true;
+free_bitmap_tags:
+	sbitmap_queue_free(&tag_set->__bitmap_tags);
+	return false;
+}
+
+void blk_mq_exit_shared_sbitmap(struct blk_mq_tag_set *tag_set)
+{
+	if (tag_set->flags & BLK_MQ_F_TAG_BITMAP_ALLOCATED) {
+		sbitmap_queue_free(&tag_set->__bitmap_tags);
+		sbitmap_queue_free(&tag_set->__breserved_tags);
+		tag_set->flags &= ~BLK_MQ_F_TAG_BITMAP_ALLOCATED;
+	}
+}
+
+bool blk_mq_init_sched_shared_sbitmap(struct blk_mq_tag_set *tag_set,
+				      unsigned long nr_requests)
+{
+	unsigned int depth = nr_requests -tag_set->reserved_tags;
+	int alloc_policy = BLK_MQ_FLAG_TO_ALLOC_POLICY(tag_set->flags);
+	bool round_robin = alloc_policy == BLK_TAG_ALLOC_RR;
+	int node = tag_set->numa_node;
+
+	if (tag_set->flags & BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED)
+		return false;
+	if (bt_alloc(&tag_set->__sched_bitmap_tags, depth, round_robin, node))
+		return false;
+	if (bt_alloc(&tag_set->__sched_breserved_tags, tag_set->reserved_tags,
+		     round_robin, node))
+		goto free_bitmap_tags;
+
+	tag_set->flags |= BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED;
+	return true;
+free_bitmap_tags:
+	sbitmap_queue_free(&tag_set->__sched_bitmap_tags);
+	return false;
+}
+
+void blk_mq_exit_shared_sched_sbitmap(struct blk_mq_tag_set *tag_set)
+{
+	if (tag_set->flags & BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED) {
+		sbitmap_queue_free(&tag_set->__sched_bitmap_tags);
+		sbitmap_queue_free(&tag_set->__sched_breserved_tags);
+		tag_set->flags &= ~BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED;
+	}
+}
+
+struct blk_mq_tags *blk_mq_init_tags(struct blk_mq_tag_set *set,
+				     unsigned int total_tags,
 				     unsigned int reserved_tags,
 				     int node, int alloc_policy)
 {
@@ -476,6 +542,8 @@  struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 	tags->nr_tags = total_tags;
 	tags->nr_reserved_tags = reserved_tags;
 
+	if (blk_mq_is_sbitmap_shared(set))
+		return tags;
 	if (blk_mq_init_bitmap_tags(tags, node, alloc_policy) < 0) {
 		kfree(tags);
 		tags = NULL;
@@ -485,8 +553,10 @@  struct blk_mq_tags *blk_mq_init_tags(unsigned int total_tags,
 
 void blk_mq_free_tags(struct blk_mq_tags *tags)
 {
-	sbitmap_queue_free(&tags->bitmap_tags);
-	sbitmap_queue_free(&tags->breserved_tags);
+	if (tags->bitmap_tags == &tags->__bitmap_tags)
+		sbitmap_queue_free(&tags->__bitmap_tags);
+	if (tags->breserved_tags == &tags->__breserved_tags)
+		sbitmap_queue_free(&tags->__breserved_tags);
 	kfree(tags);
 }
 
@@ -536,7 +606,7 @@  int blk_mq_tag_update_depth(struct blk_mq_hw_ctx *hctx,
 		 * Don't need (or can't) update reserved tags here, they
 		 * remain static and should never need resizing.
 		 */
-		sbitmap_queue_resize(&tags->bitmap_tags,
+		sbitmap_queue_resize(tags->bitmap_tags,
 				tdepth - tags->nr_reserved_tags);
 	}
 
diff --git a/block/blk-mq-tag.h b/block/blk-mq-tag.h
index 6c0f7c9ce9f6..9463b878462f 100644
--- a/block/blk-mq-tag.h
+++ b/block/blk-mq-tag.h
@@ -13,8 +13,11 @@  struct blk_mq_tags {
 
 	atomic_t active_queues;
 
-	struct sbitmap_queue bitmap_tags;
-	struct sbitmap_queue breserved_tags;
+	struct sbitmap_queue *bitmap_tags;
+	struct sbitmap_queue *breserved_tags;
+
+	struct sbitmap_queue __bitmap_tags;
+	struct sbitmap_queue __breserved_tags;
 
 	struct request **rqs;
 	struct request **static_rqs;
@@ -22,7 +25,15 @@  struct blk_mq_tags {
 };
 
 
-extern struct blk_mq_tags *blk_mq_init_tags(unsigned int nr_tags, unsigned int reserved_tags, int node, int alloc_policy);
+extern bool blk_mq_init_shared_sbitmap(struct blk_mq_tag_set *tag_set);
+extern void blk_mq_exit_shared_sbitmap(struct blk_mq_tag_set *tag_set);
+extern bool blk_mq_init_sched_shared_sbitmap(struct blk_mq_tag_set *tag_set,
+					     unsigned long nr_requests);
+extern void blk_mq_exit_shared_sched_sbitmap(struct blk_mq_tag_set *tag_set);
+extern struct blk_mq_tags *blk_mq_init_tags(struct blk_mq_tag_set *tag_set,
+					    unsigned int nr_tags,
+					    unsigned int reserved_tags,
+					    int node, int alloc_policy);
 extern void blk_mq_free_tags(struct blk_mq_tags *tags);
 
 extern unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data);
diff --git a/block/blk-mq.c b/block/blk-mq.c
index 91950d3e436a..016f8401cfb9 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -1095,7 +1095,7 @@  static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
 		struct sbitmap_queue *sbq;
 
 		list_del_init(&wait->entry);
-		sbq = &hctx->tags->bitmap_tags;
+		sbq = hctx->tags->bitmap_tags;
 		atomic_dec(&sbq->ws_active);
 	}
 	spin_unlock(&hctx->dispatch_wait_lock);
@@ -1113,7 +1113,7 @@  static int blk_mq_dispatch_wake(wait_queue_entry_t *wait, unsigned mode,
 static bool blk_mq_mark_tag_wait(struct blk_mq_hw_ctx *hctx,
 				 struct request *rq)
 {
-	struct sbitmap_queue *sbq = &hctx->tags->bitmap_tags;
+	struct sbitmap_queue *sbq = hctx->tags->bitmap_tags;
 	struct wait_queue_head *wq;
 	wait_queue_entry_t *wait;
 	bool ret;
@@ -2081,7 +2081,6 @@  void blk_mq_free_rq_map(struct blk_mq_tags *tags)
 	tags->rqs = NULL;
 	kfree(tags->static_rqs);
 	tags->static_rqs = NULL;
-
 	blk_mq_free_tags(tags);
 }
 
@@ -2097,7 +2096,7 @@  struct blk_mq_tags *blk_mq_alloc_rq_map(struct blk_mq_tag_set *set,
 	if (node == NUMA_NO_NODE)
 		node = set->numa_node;
 
-	tags = blk_mq_init_tags(nr_tags, reserved_tags, node,
+	tags = blk_mq_init_tags(set, nr_tags, reserved_tags, node,
 				BLK_MQ_FLAG_TO_ALLOC_POLICY(set->flags));
 	if (!tags)
 		return NULL;
@@ -2954,8 +2953,10 @@  static int __blk_mq_alloc_rq_maps(struct blk_mq_tag_set *set)
 	return 0;
 
 out_unwind:
-	while (--i >= 0)
+	while (--i >= 0) {
 		blk_mq_free_rq_map(set->tags[i]);
+		set->tags[i] = NULL;
+	}
 
 	return -ENOMEM;
 }
@@ -3100,6 +3101,20 @@  int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set)
 	if (ret)
 		goto out_free_mq_map;
 
+	if (blk_mq_is_sbitmap_shared(set)) {
+		if (!blk_mq_init_shared_sbitmap(set)) {
+			ret = -ENOMEM;
+			goto out_free_mq_map;
+		}
+
+		for (i = 0; i < set->nr_hw_queues; i++) {
+			struct blk_mq_tags *tags = set->tags[i];
+
+			tags->bitmap_tags = &set->__bitmap_tags;
+			tags->breserved_tags = &set->__breserved_tags;
+		}
+	}
+
 	mutex_init(&set->tag_list_lock);
 	INIT_LIST_HEAD(&set->tag_list);
 
@@ -3123,6 +3138,9 @@  void blk_mq_free_tag_set(struct blk_mq_tag_set *set)
 	for (i = 0; i < nr_hw_queues(set); i++)
 		blk_mq_free_map_and_requests(set, i);
 
+	blk_mq_exit_shared_sched_sbitmap(set);
+	blk_mq_exit_shared_sbitmap(set);
+
 	for (j = 0; j < set->nr_maps; j++) {
 		kfree(set->map[j].mq_map);
 		set->map[j].mq_map = NULL;
@@ -3137,6 +3155,7 @@  int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 {
 	struct blk_mq_tag_set *set = q->tag_set;
 	struct blk_mq_hw_ctx *hctx;
+	bool sched_tags = false;
 	int i, ret;
 
 	if (!set)
@@ -3160,6 +3179,7 @@  int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 			ret = blk_mq_tag_update_depth(hctx, &hctx->tags, nr,
 							false);
 		} else {
+			sched_tags = true;
 			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
 							nr, true);
 		}
@@ -3169,8 +3189,43 @@  int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 			q->elevator->type->ops.depth_updated(hctx);
 	}
 
-	if (!ret)
+	/*
+	 * if ret is 0, all queues should have been updated to the same depth
+	 * if not, then maybe some have been updated - yuk, need to handle this for shared sbitmap...
+	 * if some are updated, we should probably roll back the change altogether. FIXME
+	 */
+	if (!ret) {
+		if (blk_mq_is_sbitmap_shared(set)) {
+			if (sched_tags) {
+				blk_mq_exit_shared_sched_sbitmap(set);
+				if (!blk_mq_init_sched_shared_sbitmap(set, nr))
+					return -ENOMEM; /* fixup error handling */
+
+				queue_for_each_hw_ctx(q, hctx, i) {
+					hctx->sched_tags->bitmap_tags =
+						&set->__sched_bitmap_tags;
+					hctx->sched_tags->breserved_tags =
+						&set->__sched_breserved_tags;
+				}
+			} else {
+				blk_mq_exit_shared_sbitmap(set);
+				if (!blk_mq_init_shared_sbitmap(set))
+					return -ENOMEM; /* fixup error handling */
+
+				queue_for_each_hw_ctx(q, hctx, i) {
+					hctx->tags->bitmap_tags =
+						&set->__bitmap_tags;
+					hctx->tags->breserved_tags =
+						&set->__breserved_tags;
+				}
+			}
+		}
 		q->nr_requests = nr;
+	}
+	/*
+	 * if ret != 0, q->nr_requests would not be updated, yet the depth
+	 * for some hctx may have changed - is that right?
+	 */
 
 	blk_mq_unquiesce_queue(q);
 	blk_mq_unfreeze_queue(q);
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 78d38b5f2793..4c1ea206d3f4 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -166,6 +166,11 @@  struct blk_mq_alloc_data {
 	struct blk_mq_hw_ctx *hctx;
 };
 
+static inline bool blk_mq_is_sbitmap_shared(struct blk_mq_tag_set *tag_set)
+{
+	return !!(tag_set->flags & BLK_MQ_F_TAG_HCTX_SHARED);
+}
+
 static inline struct blk_mq_tags *blk_mq_tags_from_data(struct blk_mq_alloc_data *data)
 {
 	if (data->flags & BLK_MQ_REQ_INTERNAL)
diff --git a/block/kyber-iosched.c b/block/kyber-iosched.c
index 34dcea0ef637..a7a537501d70 100644
--- a/block/kyber-iosched.c
+++ b/block/kyber-iosched.c
@@ -359,7 +359,7 @@  static unsigned int kyber_sched_tags_shift(struct request_queue *q)
 	 * All of the hardware queues have the same depth, so we can just grab
 	 * the shift of the first one.
 	 */
-	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags.sb.shift;
+	return q->queue_hw_ctx[0]->sched_tags->bitmap_tags->sb.shift;
 }
 
 static struct kyber_queue_data *kyber_queue_data_alloc(struct request_queue *q)
@@ -502,7 +502,7 @@  static int kyber_init_hctx(struct blk_mq_hw_ctx *hctx, unsigned int hctx_idx)
 	khd->batching = 0;
 
 	hctx->sched_data = khd;
-	sbitmap_queue_min_shallow_depth(&hctx->sched_tags->bitmap_tags,
+	sbitmap_queue_min_shallow_depth(hctx->sched_tags->bitmap_tags,
 					kqd->async_depth);
 
 	return 0;
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index 147185394a25..10c9ed3dbe80 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -109,6 +109,12 @@  struct blk_mq_tag_set {
 	unsigned int		flags;		/* BLK_MQ_F_* */
 	void			*driver_data;
 
+	struct sbitmap_queue	__bitmap_tags;
+	struct sbitmap_queue	__breserved_tags;
+
+	struct sbitmap_queue	__sched_bitmap_tags;
+	struct sbitmap_queue	__sched_breserved_tags;
+
 	struct blk_mq_tags	**tags;
 
 	struct mutex		tag_list_lock;
@@ -226,6 +232,9 @@  struct blk_mq_ops {
 enum {
 	BLK_MQ_F_SHOULD_MERGE	= 1 << 0,
 	BLK_MQ_F_TAG_QUEUE_SHARED	= 1 << 1,
+	BLK_MQ_F_TAG_HCTX_SHARED	= 1 << 2,
+	BLK_MQ_F_TAG_BITMAP_ALLOCATED	= 1 << 3,
+	BLK_MQ_F_TAG_SCHED_BITMAP_ALLOCATED = 1 << 4,
 	BLK_MQ_F_BLOCKING	= 1 << 5,
 	BLK_MQ_F_NO_SCHED	= 1 << 6,
 	BLK_MQ_F_ALLOC_POLICY_START_BIT = 8,