From mboxrd@z Thu Jan  1 00:00:00 1970
From: bvanassche@acm.org (Bart Van Assche)
Date: Wed, 05 Sep 2018 08:57:17 -0700
Subject: [PATCH 2/3] blk-core: introduce queue close feature
In-Reply-To: <1536120586-3378-3-git-send-email-jianchao.w.wang@oracle.com>
References: <1536120586-3378-1-git-send-email-jianchao.w.wang@oracle.com>
 <1536120586-3378-3-git-send-email-jianchao.w.wang@oracle.com>
Message-ID: <1536163037.11534.6.camel@acm.org>

On Wed, 2018-09-05@12:09 +0800, Jianchao Wang wrote:
> blk queue freeze is often used to prevent new IO from entering
> request queue. However, becuase we kill the percpu-ref
> q_usage_counter when freeze queue, we have to drain the request
> queue when unfreeze. This is unnecessary for just preventing new
> IO. In addition, If there is IO timeout or other issue when unfreeze
> the queue, the scenario could be very tricky.
> 
> So we introduce BLK_QUEUE_GATE_CLOSED to implement a light-weight
> queue close feature base on the queue_gate to prevent new IO from
> comming in queue which will not need to drain the queue any more.

Does the "queue gate close" feature cause blk_get_request() /
blk_mq_get_request() to block until blk_clear_queue_closed() is called? If
so, I think we need a better name for this feature. How about calling these
two operations suspend and resume?

Thanks,

Bart.