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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 868f2f0b72 ("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: Bart Van Assche <bvanassche@acm.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Bart Van Assche 2019-10-25 09:50:10 -07:00 committed by Jens Axboe
parent ac0d6b926e
commit f7e76dbc24
1 changed files with 30 additions and 17 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

47
block/blk-mq.c
View File

@ -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);