linux-kernel - [PATCH v2 for-6.18/block 06/10] blk-mq: split bitmap grow and resize case in blk_mq_update_nr

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Message-Id: <20250910080445.239096-7-yukuai1@huaweicloud.com>
Date: Wed, 10 Sep 2025 16:04:41 +0800
From: Yu Kuai <yukuai1@...weicloud.com>
To: axboe@...nel.dk,
	nilay@...ux.ibm.com,
	ming.lei@...hat.com
Cc: linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	yukuai3@...wei.com,
	yi.zhang@...wei.com,
	yangerkun@...wei.com,
	johnny.chenyi@...wei.com
Subject: [PATCH v2 for-6.18/block 06/10] blk-mq: split bitmap grow and resize case in blk_mq_update_nr_requests()

From: Yu Kuai <yukuai3@...wei.com>

No functional changes are intended, make code cleaner and prepare to fix
the grow case in following patches.

Signed-off-by: Yu Kuai <yukuai3@...wei.com>
---
 block/blk-mq.c | 39 +++++++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 12 deletions(-)

diff --git a/block/blk-mq.c b/block/blk-mq.c
index 80c20700bce8..299aac458185 100644
--- a/block/blk-mq.c
+++ b/block/blk-mq.c
@@ -4936,25 +4936,40 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
 	blk_mq_quiesce_queue(q);
 
 	if (blk_mq_is_shared_tags(set->flags)) {
+		/*
+		 * Shared tags, for sched tags, we allocate max initially hence
+		 * tags can't grow, see blk_mq_alloc_sched_tags().
+		 */
 		if (q->elevator)
 			blk_mq_tag_update_sched_shared_tags(q);
 		else
 			blk_mq_tag_resize_shared_tags(set, nr);
-	} else {
+	} else if (!q->elevator) {
+		/*
+		 * Non-shared hardware tags, nr is already checked from
+		 * queue_requests_store() and tags can't grow.
+		 */
 		queue_for_each_hw_ctx(q, hctx, i) {
 			if (!hctx->tags)
 				continue;
-			/*
-			 * If we're using an MQ scheduler, just update the
-			 * scheduler queue depth. This is similar to what the
-			 * old code would do.
-			 */
-			if (hctx->sched_tags)
-				ret = blk_mq_tag_update_depth(hctx,
-							&hctx->sched_tags, nr);
-			else
-				ret = blk_mq_tag_update_depth(hctx,
-							&hctx->tags, nr);
+			sbitmap_queue_resize(&hctx->tags->bitmap_tags,
+				nr - hctx->tags->nr_reserved_tags);
+		}
+	} else if (nr <= q->elevator->et->nr_requests) {
+		/* Non-shared sched tags, and tags don't grow. */
+		queue_for_each_hw_ctx(q, hctx, i) {
+			if (!hctx->sched_tags)
+				continue;
+			sbitmap_queue_resize(&hctx->sched_tags->bitmap_tags,
+				nr - hctx->sched_tags->nr_reserved_tags);
+		}
+	} else {
+		/* Non-shared sched tags, and tags grow */
+		queue_for_each_hw_ctx(q, hctx, i) {
+			if (!hctx->sched_tags)
+				continue;
+			ret = blk_mq_tag_update_depth(hctx, &hctx->sched_tags,
+						      nr);
 			if (ret)
 				goto out;
 		}
-- 
2.39.2