[PATCH v2 1/2] blk-mq: add tagset quiesce interface

[Chao Leng]

On 2022/10/17 21:39, Christoph Hellwig wrote:
> On Thu, Oct 13, 2022 at 05:44:49PM +0800, Chao Leng wrote:
>> +	rcu = kvmalloc(count * sizeof(*rcu), GFP_KERNEL);
>> +	if (rcu) {
>> +		list_for_each_entry(q, &set->tag_list, tag_set_list) {
>> +			if (blk_queue_noquiesced(q))
>> +				continue;
>> +
>> +			init_rcu_head(&rcu[i].head);
>> +			init_completion(&rcu[i].completion);
>> +			call_srcu(q->srcu, &rcu[i].head, wakeme_after_rcu);
>> +			i++;
>> +		}
>> +
>> +		for (i = 0; i < count; i++) {
>> +			wait_for_completion(&rcu[i].completion);
>> +			destroy_rcu_head(&rcu[i].head);
>> +		}
>> +		kvfree(rcu);
>> +	} else {
>> +		list_for_each_entry(q, &set->tag_list, tag_set_list)
>> +			synchronize_srcu(q->srcu);
>> +	}
> 
> Having to allocate a struct rcu_synchronize for each of the potentially
> many queues here is a bit sad.
> 
> Pull just explained the start_poll_synchronize_rcu interfaces at ALPSS
> last week, so I wonder if something like that would also be feasible
> for SRCU, as that would come in really handy here.
Using start_poll_synchronize_rcu will reduce some memory.
This is a good idea.
> 
> .
>