Re: [PATCH 2/3] blk-mq: remove RQF_ELVPRIV

From: Jens Axboe <axboe@kernel.dk>
To: Ming Lei <ming.lei@redhat.com>, Christoph Hellwig <hch@lst.de>
Cc: linux-block@vger.kernel.org
Subject: Re: [PATCH 2/3] blk-mq: remove RQF_ELVPRIV
Date: Thu, 18 May 2023 19:39:04 -0600	[thread overview]
Message-ID: <a849d530-a975-9b63-702a-6c29c8f54bee@kernel.dk> (raw)
In-Reply-To: <ZGYmK/y/TXuYk3tN@ovpn-8-21.pek2.redhat.com>

On 5/18/23 7:20 AM, Ming Lei wrote:
> On Thu, May 18, 2023 at 03:06:32PM +0200, Christoph Hellwig wrote:
>> On Thu, May 18, 2023 at 03:11:12PM +0800, Ming Lei wrote:
>>>> -		if ((rq->rq_flags & RQF_ELVPRIV) && e->type->ops.requeue_request)
>>>> +		if (e->type->ops.requeue_request)
>>>>  			e->type->ops.requeue_request(rq);
>>>
>>> The above actually changes current behavior since RQF_ELVPRIV is only set
>>> iff the following condition is true:
>>>
>>> 	(rq->rq_flags & RQF_ELV) && !op_is_flush(rq->cmd_flags) &&
>>> 		e->type->ops.prepare_request.
>>
>> It would require an I/O scheduler that implements .requeue_request but
>> not .prepare_request, which doesn't exist and also is rather pointless as
>> this .requeue_request method would never get called in the current code.
>>
>> So no, no behavior change in practice.
> 
> Fair enough, just found that all three schedulers have implemented
> e->type->ops.prepare_request.

We should probably make this requirement explicit though, seems
very fragile to depend on it just because it's the status quo.

-- 
Jens Axboe