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

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Date:   Thu, 6 Sep 2018 09:31:06 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Bart Van Assche <bvanassche@....org>, 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

Hi Bart

On 09/05/2018 11:57 PM, Bart Van Assche wrote:
> 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? 

Yes. It works in blk_queue_enter. So it could cover blk_mq_get_request

If
> so, I think we need a better name for this feature. How about calling these
> two operations suspend and resume?

I'm open for it. :)

> 
> Thanks,
> 
> Bart.
>