Commit f7e76dbc authored by Bart Van Assche's avatar Bart Van Assche Committed by Jens Axboe
Browse files

block: Reduce the amount of memory used for tag sets 



Instead of allocating an array of size nr_cpu_ids for set->tags, allocate
an array of size set->nr_hw_queues. This patch improves behavior that was
introduced by commit 868f2f0b ("blk-mq: dynamic h/w context count").

Reallocating tag sets from inside __blk_mq_update_nr_hw_queues() is safe
because:
- All request queues that share the tag sets are frozen before the tag sets
  are reallocated.
- blk_mq_queue_tag_busy_iter() holds q->q_usage_counter while active and
  hence is serialized against __blk_mq_update_nr_hw_queues().

Cc: Keith Busch <keith.busch@intel.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Ming Lei <ming.lei@redhat.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: default avatarBart Van Assche <bvanassche@acm.org>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent ac0d6b92

block/blk-mq.c

+30 −17
Original line number Diff line number Diff line
@@ -2833,19 +2833,6 @@ static void blk_mq_realloc_hw_ctxs(struct blk_mq_tag_set *set, 
	mutex_unlock(&q->sysfs_lock);

}



/*

 * Maximum number of hardware queues we support. For single sets, we'll never

 * have more than the CPUs (software queues). For multiple sets, the tag_set

 * user may have set ->nr_hw_queues larger.

 */

static unsigned int nr_hw_queues(struct blk_mq_tag_set *set)

{

	if (set->nr_maps == 1)

		return nr_cpu_ids;



	return max(set->nr_hw_queues, nr_cpu_ids);

}



struct request_queue *blk_mq_init_allocated_queue(struct blk_mq_tag_set *set,

						  struct request_queue *q,

						  bool elevator_init)
@@ -3012,6 +2999,29 @@ static int blk_mq_update_queue_map(struct blk_mq_tag_set *set) 
	}

}



static int blk_mq_realloc_tag_set_tags(struct blk_mq_tag_set *set,

				  int cur_nr_hw_queues, int new_nr_hw_queues)

{

	struct blk_mq_tags **new_tags;



	if (cur_nr_hw_queues >= new_nr_hw_queues)

		return 0;



	new_tags = kcalloc_node(new_nr_hw_queues, sizeof(struct blk_mq_tags *),

				GFP_KERNEL, set->numa_node);

	if (!new_tags)

		return -ENOMEM;



	if (set->tags)

		memcpy(new_tags, set->tags, cur_nr_hw_queues *

		       sizeof(*set->tags));

	kfree(set->tags);

	set->tags = new_tags;

	set->nr_hw_queues = new_nr_hw_queues;



	return 0;

}



/*

 * Alloc a tag set to be associated with one or more request queues.

 * May fail with EINVAL for various error conditions. May adjust the
@@ -3065,9 +3075,7 @@ int blk_mq_alloc_tag_set(struct blk_mq_tag_set *set) 
	if (set->nr_maps == 1 && set->nr_hw_queues > nr_cpu_ids)

		set->nr_hw_queues = nr_cpu_ids;



	set->tags = kcalloc_node(nr_hw_queues(set), sizeof(struct blk_mq_tags *),

				 GFP_KERNEL, set->numa_node);

	if (!set->tags)

	if (blk_mq_realloc_tag_set_tags(set, 0, set->nr_hw_queues) < 0)

		return -ENOMEM;



	ret = -ENOMEM;
@@ -3108,7 +3116,7 @@ void blk_mq_free_tag_set(struct blk_mq_tag_set *set) 
{

	int i, j;



	for (i = 0; i < nr_hw_queues(set); i++)

	for (i = 0; i < set->nr_hw_queues; i++)

		blk_mq_free_map_and_requests(set, i);



	for (j = 0; j < set->nr_maps; j++) {
@@ -3266,6 +3274,10 @@ static void __blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, 
		blk_mq_sysfs_unregister(q);

	}



	if (blk_mq_realloc_tag_set_tags(set, set->nr_hw_queues, nr_hw_queues) <

	    0)

		goto reregister;



	prev_nr_hw_queues = set->nr_hw_queues;

	set->nr_hw_queues = nr_hw_queues;

	blk_mq_update_queue_map(set);
@@ -3282,6 +3294,7 @@ fallback: 
		blk_mq_map_swqueue(q);

	}



reregister:

	list_for_each_entry(q, &set->tag_list, tag_set_list) {

		blk_mq_sysfs_register(q);

		blk_mq_debugfs_register_hctxs(q);

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