Re: [PATCH 3/8] blk-mq: move the srcu_struct used for quiescing to the tagset

From: Keith Busch <kbusch@kernel.org>
To: Christoph Hellwig <hch@lst.de>
Cc: Jens Axboe <axboe@kernel.dk>, Sagi Grimberg <sagi@grimberg.me>,
	Chao Leng <lengchao@huawei.com>, Ming Lei <ming.lei@redhat.com>,
	linux-nvme@lists.infradead.org, linux-block@vger.kernel.org
Subject: Re: [PATCH 3/8] blk-mq: move the srcu_struct used for quiescing to the tagset
Date: Thu, 20 Oct 2022 11:26:55 -0600	[thread overview]
Message-ID: <Y1GE37ujxcfRn7Tm@kbusch-mbp.dhcp.thefacebook.com> (raw)
In-Reply-To: <20221020105608.1581940-4-hch@lst.de>

On Thu, Oct 20, 2022 at 12:56:03PM +0200, Christoph Hellwig wrote:
> All I/O submissions have fairly similar latencies, and a tagset-wide
> quiesce is a fairly common operation.  Becuase there are a lot less

s/Becuase/Because

> @@ -501,6 +502,8 @@ enum hctx_type {
>   * @tag_list_lock: Serializes tag_list accesses.
>   * @tag_list:	   List of the request queues that use this tag set. See also
>   *		   request_queue.tag_set_list.
> + * @srcu:	   Use as lock when type of the request queue is blocking
> + *		   (BLK_MQ_F_BLOCKING). Must be the last member

Since you're not dealing with flexible arrays anymore, I don't think
srcu strictly needs to be the last member.

The code looks great, though!

Reviewed-by: Keith Busch <kbusch@kernel.org>

>   */
>  struct blk_mq_tag_set {
>  	struct blk_mq_queue_map	map[HCTX_MAX_TYPES];
> @@ -521,6 +524,7 @@ struct blk_mq_tag_set {
>  
>  	struct mutex		tag_list_lock;
>  	struct list_head	tag_list;
> +	struct srcu_struct	srcu;
>  };