linux-kernel - Re: [PATCH 2/3] blk-core: introduce queue close feature

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Date:   Wed, 05 Sep 2018 08:57:17 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Jianchao Wang <jianchao.w.wang@...cle.com>, axboe@...nel.dk,
        ming.lei@...hat.com, bart.vanassche@....com, sagi@...mberg.me,
        keith.busch@...el.com, jthumshirn@...e.de, jsmart2021@...il.com
Cc:     linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH 2/3] blk-core: introduce queue close feature

On Wed, 2018-09-05 at 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.