blk-mq: Use shared tags for shared sbitmap support

Currently we use separate sbitmap pairs and active_queues atomic_t for
shared sbitmap support.

However a full sets of static requests are used per HW queue, which is
quite wasteful, considering that the total number of requests usable at
any given time across all HW queues is limited by the shared sbitmap depth.

As such, it is considerably more memory efficient in the case of shared
sbitmap to allocate a set of static rqs per tag set or request queue, and
not per HW queue.

So replace the sbitmap pairs and active_queues atomic_t with a shared
tags per tagset and request queue, which will hold a set of shared static
rqs.

Since there is now no valid HW queue index to be passed to the blk_mq_ops
.init and .exit_request callbacks, pass an invalid index token. This
changes the semantics of the APIs, such that the callback would need to
validate the HW queue index before using it. Currently no user of shared
sbitmap actually uses the HW queue index (as would be expected).

Signed-off-by: John Garry <john.garry@huawei.com>
Reviewed-by: Ming Lei <ming.lei@redhat.com>
Link: https://lore.kernel.org/r/1633429419-228500-13-git-send-email-john.garry@huawei.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

1 files changed, 3 insertions, 4 deletions

diff --git a/block/blk-mq.h b/block/blk-mq.h
index bcb0ca89d37a..8824ae03215a 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -54,7 +54,7 @@ void blk_mq_put_rq_ref(struct request *rq);
  */
 void blk_mq_free_rqs(struct blk_mq_tag_set *set, struct blk_mq_tags *tags,
 		     unsigned int hctx_idx);
-void blk_mq_free_rq_map(struct blk_mq_tags *tags, unsigned int flags);
+void blk_mq_free_rq_map(struct blk_mq_tags *tags);
 struct blk_mq_tags *blk_mq_alloc_map_and_rqs(struct blk_mq_tag_set *set,
 				unsigned int hctx_idx, unsigned int depth);
 void blk_mq_free_map_and_rqs(struct blk_mq_tag_set *set,
@@ -330,17 +330,16 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 
 	if (blk_mq_is_sbitmap_shared(hctx->flags)) {
 		struct request_queue *q = hctx->queue;
-		struct blk_mq_tag_set *set = q->tag_set;
 
 		if (!test_bit(QUEUE_FLAG_HCTX_ACTIVE, &q->queue_flags))
 			return true;
-		users = atomic_read(&set->active_queues_shared_sbitmap);
 	} else {
 		if (!test_bit(BLK_MQ_S_TAG_ACTIVE, &hctx->state))
 			return true;
-		users = atomic_read(&hctx->tags->active_queues);
 	}
 
+	users = atomic_read(&hctx->tags->active_queues);
+
 	if (!users)
 		return true;