linux-kernel - Re: [PATCH v2 10/11] blk-mq: Use shared tags for shared sbitmap support

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Date:   Mon, 23 Aug 2021 09:55:44 +0100
From:   John Garry <john.garry@...wei.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        "jejb@...ux.ibm.com" <jejb@...ux.ibm.com>,
        "martin.petersen@...cle.com" <martin.petersen@...cle.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-scsi@...r.kernel.org" <linux-scsi@...r.kernel.org>,
        "kashyap.desai@...adcom.com" <kashyap.desai@...adcom.com>,
        "hare@...e.de" <hare@...e.de>
Subject: Re: [PATCH v2 10/11] blk-mq: Use shared tags for shared sbitmap
 support

On 18/08/2021 09:16, Ming Lei wrote:
>> ret = blk_mq_alloc_rqs(set, tags, 0, set->queue_depth);
>> +	if (ret) {
>> +		blk_mq_exit_sched_shared_sbitmap(queue);
>> +		return ret;
> There are two such patterns for allocate rq map and request pool
> together, please put them into one helper(such as blk_mq_alloc_map_and_rqs)
> which can return the allocated tags and handle failure inline. Also we may
> convert current users into this helper.
> 
>>   	}

Hi Ming,

Do you have a preference for the API:

int blk_mq_alloc_map_and_rqs(struct blk_mq_tag_set *set, struct 
blk_mq_tags **tags, unsigned int hctx_idx, unsigned int depth);

void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
  struct blk_mq_tags **tags, unsigned int hctx_idx);


or

struct blk_mq_tags *blk_mq_alloc_map_and_rqs(struct blk_mq_tag_set *set,
unsigned int hctx_idx, unsigned int depth);

void blk_mq_free_map_and_requests(struct blk_mq_tag_set *set,
  struct blk_mq_tags *tags, unsigned int hctx_idx);


The advantage of the first is that we don't need the pattern:
blk_mq_free_map_and_requests(tags)
tags = NULL;

But then passing struct blk_mq_tags ** is a bit overly complicated.

Thanks,
John