[PATCH RFC 1/7] blk-mq: factor out a structure from blk_mq_tags to control tag sharing

[Yu Kuai <yukuai1@xxxxxxxxxxxxxxx>]

From: Yu Kuai <yukuai3@xxxxxxxxxx>

Currently tags is fair shared, and the new structure contains only one
field active_queues. There are no functional changes and prepare to
refactor tag sharing.

Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
---
 block/blk-mq-debugfs.c |  2 +-
 block/blk-mq-tag.c     |  8 ++++----
 block/blk-mq.h         |  2 +-
 include/linux/blk-mq.h | 10 ++++++++--
 4 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/block/blk-mq-debugfs.c b/block/blk-mq-debugfs.c
index c3b5930106b2..431aaa3eb181 100644
--- a/block/blk-mq-debugfs.c
+++ b/block/blk-mq-debugfs.c
@@ -401,7 +401,7 @@ static void blk_mq_debugfs_tags_show(struct seq_file *m,
 	seq_printf(m, "nr_tags=%u\n", tags->nr_tags);
 	seq_printf(m, "nr_reserved_tags=%u\n", tags->nr_reserved_tags);
 	seq_printf(m, "active_queues=%d\n",
-		   READ_ONCE(tags->active_queues));
+		   READ_ONCE(tags->ctl.active_queues));
 
 	seq_puts(m, "\nbitmap_tags:\n");
 	sbitmap_queue_show(&tags->bitmap_tags, m);
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index cc57e2dd9a0b..fe41a0d34fc0 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -57,8 +57,8 @@ void __blk_mq_tag_busy(struct blk_mq_hw_ctx *hctx)
 	}
 
 	spin_lock_irq(&tags->lock);
-	users = tags->active_queues + 1;
-	WRITE_ONCE(tags->active_queues, users);
+	users = tags->ctl.active_queues + 1;
+	WRITE_ONCE(tags->ctl.active_queues, users);
 	blk_mq_update_wake_batch(tags, users);
 	spin_unlock_irq(&tags->lock);
 }
@@ -94,8 +94,8 @@ void __blk_mq_tag_idle(struct blk_mq_hw_ctx *hctx)
 	}
 
 	spin_lock_irq(&tags->lock);
-	users = tags->active_queues - 1;
-	WRITE_ONCE(tags->active_queues, users);
+	users = tags->ctl.active_queues - 1;
+	WRITE_ONCE(tags->ctl.active_queues, users);
 	blk_mq_update_wake_batch(tags, users);
 	spin_unlock_irq(&tags->lock);
 
diff --git a/block/blk-mq.h b/block/blk-mq.h
index 1743857e0b01..ca1c13127868 100644
--- a/block/blk-mq.h
+++ b/block/blk-mq.h
@@ -412,7 +412,7 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
 			return true;
 	}
 
-	users = READ_ONCE(hctx->tags->active_queues);
+	users = READ_ONCE(hctx->tags->ctl.active_queues);
 	if (!users)
 		return true;
 
diff --git a/include/linux/blk-mq.h b/include/linux/blk-mq.h
index f401067ac03a..8d2cd6b9d305 100644
--- a/include/linux/blk-mq.h
+++ b/include/linux/blk-mq.h
@@ -733,13 +733,16 @@ struct request *blk_mq_alloc_request_hctx(struct request_queue *q,
 		blk_opf_t opf, blk_mq_req_flags_t flags,
 		unsigned int hctx_idx);
 
+struct tag_sharing_ctl {
+	unsigned int active_queues;
+};
+
 /*
  * Tag address space map.
  */
 struct blk_mq_tags {
 	unsigned int nr_tags;
 	unsigned int nr_reserved_tags;
-	unsigned int active_queues;
 
 	struct sbitmap_queue bitmap_tags;
 	struct sbitmap_queue breserved_tags;
@@ -750,9 +753,12 @@ struct blk_mq_tags {
 
 	/*
 	 * used to clear request reference in rqs[] before freeing one
-	 * request pool
+	 * request pool, and to protect tag_sharing_ctl.
 	 */
 	spinlock_t lock;
+
+	/* used when tags is shared for multiple request_queue or hctx. */
+	struct tag_sharing_ctl ctl;
 };
 
 static inline struct request *blk_mq_tag_to_rq(struct blk_mq_tags *tags,
-- 
2.39.2