Re: [PATCH for-6.18/block 06/10] blk-mq: split bitmap grow and resize case in blk_mq_update_nr_requests()

[Nilay Shroff <nilay@linux.ibm.com>]

On 9/8/25 11:45 AM, Yu Kuai wrote:
> From: Yu Kuai <yukuai3@huawei.com>
> 
> No functional changes are intended, make code cleaner and prepare to fix
> the grow case in following patches.
> 
> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
> ---
>  block/blk-mq.c | 28 ++++++++++++++++------------
>  1 file changed, 16 insertions(+), 12 deletions(-)
> 
> diff --git a/block/blk-mq.c b/block/blk-mq.c
> index 1ff6370f7314..82fa81036115 100644
> --- a/block/blk-mq.c
> +++ b/block/blk-mq.c
> @@ -4931,21 +4931,25 @@ int blk_mq_update_nr_requests(struct request_queue *q, unsigned int nr)
>  			blk_mq_tag_update_sched_shared_tags(q);
>  		else
>  			blk_mq_tag_resize_shared_tags(set, nr);
> -	} else {
> +	} else if (!q->elevator) {
>  		queue_for_each_hw_ctx(q, hctx, i) {
>  			if (!hctx->tags)
>  				continue;
> -			/*
> -			 * If we're using an MQ scheduler, just update the
> -			 * scheduler queue depth. This is similar to what the
> -			 * old code would do.
> -			 */
> -			if (hctx->sched_tags)
> -				ret = blk_mq_tag_update_depth(hctx,
> -							&hctx->sched_tags, nr);
> -			else
> -				ret = blk_mq_tag_update_depth(hctx,
> -							&hctx->tags, nr);
> +			sbitmap_queue_resize(&hctx->tags->bitmap_tags,
> +				nr - hctx->tags->nr_reserved_tags);
> +		}
> +	} else if (nr <= q->elevator->et->nr_requests) {
> +		queue_for_each_hw_ctx(q, hctx, i) {
> +			if (!hctx->sched_tags)
> +				continue;
> +			sbitmap_queue_resize(&hctx->sched_tags->bitmap_tags,
> +				nr - hctx->sched_tags->nr_reserved_tags);
> +		}
> +	} else {
> +		queue_for_each_hw_ctx(q, hctx, i) {
> +			if (!hctx->sched_tags)
> +				continue;
> +			blk_mq_tag_update_depth(hctx, &hctx->sched_tags, nr);
>  			if (ret)
>  				goto out;
>  		}

The above code is good however can this be bit simplified? 
It's a bit difficult to follow through all nesting and so
could it be simplified as below:

if (shared-tags) {
    if (elevator) 
       // resize sched-shared-tags bitmap
    else
       // resize shared-tags bitmap
} else { 
    // non-shared tags
    if (elevator) {
        if (new-depth-is-less-than-the-current-depth)
            // resize sched-tags bitmap
        else
            // handle sched tags grow
    } else
        // resize tags bitmap    
}

Thanks,
--Nilay