linux-kernel - Re: [PATCH 6/7] mq-deadline: add blk-mq adaptation of the deadline IO scheduler

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Message-ID: <26064b12-6434-27bd-97d2-b6a747b20a66@fb.com>
Date:   Tue, 13 Dec 2016 08:08:28 -0700
From:   Jens Axboe <axboe@...com>
To:     Bart Van Assche <bart.vanassche@...disk.com>, <axboe@...nel.dk>,
        <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>
CC:     <paolo.valente@...aro.org>, <osandov@...com>
Subject: Re: [PATCH 6/7] mq-deadline: add blk-mq adaptation of the deadline IO
 scheduler

On 12/13/2016 04:04 AM, Bart Van Assche wrote:
> On 12/08/2016 09:13 PM, Jens Axboe wrote:
>> +static int dd_init_queue(struct request_queue *q, struct elevator_type *e)
>> +{
>> +	struct deadline_data *dd;
>> +	struct elevator_queue *eq;
>> +
>> +	eq = elevator_alloc(q, e);
>> +	if (!eq)
>> +		return -ENOMEM;
>> +
>> +	dd = kzalloc_node(sizeof(*dd), GFP_KERNEL, q->node);
>> +	if (!dd) {
>> +		kobject_put(&eq->kobj);
>> +		return -ENOMEM;
>> +	}
>> +	eq->elevator_data = dd;
>> +
>> +	dd->tags = blk_mq_sched_alloc_requests(256, q->node);
>> +	if (!dd->tags) {
>> +		kfree(dd);
>> +		kobject_put(&eq->kobj);
>> +		return -ENOMEM;
>> +	}
> 
> Hello Jens,
> 
> Please add a comment that explains where the number 256 comes from.

Pulled out of my... I'll add a comment! Really this should just be
->nr_requests soft setting, the 256 is just a random sane default that I
chose for now. I had forgotten about that, thanks.

-- 
Jens Axboe