linux-kernel - Re: [PATCH v7 1/3] bio: limit bio max size

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Date:   Tue, 13 Apr 2021 09:18:00 -0700
From:   Bart Van Assche <bvanassche@....org>
To:     Changheun Lee <nanich.lee@...sung.com>, damien.lemoal@....com,
        Johannes.Thumshirn@....com, asml.silence@...il.com,
        axboe@...nel.dk, gregkh@...uxfoundation.org, hch@...radead.org,
        linux-block@...r.kernel.org, linux-kernel@...r.kernel.org,
        ming.lei@...hat.com, osandov@...com, patchwork-bot@...nel.org,
        tj@...nel.org, tom.leiming@...il.com
Cc:     jisoo2146.oh@...sung.com, junho89.kim@...sung.com,
        mj0123.lee@...sung.com, seunghwan.hyun@...sung.com,
        sookwan7.kim@...sung.com, woosung2.lee@...sung.com,
        yt0928.kim@...sung.com
Subject: Re: [PATCH v7 1/3] bio: limit bio max size

On 4/12/21 7:55 PM, Changheun Lee wrote:
> +unsigned int bio_max_size(struct bio *bio)
> +{
> +	struct request_queue *q = bio->bi_bdev->bd_disk->queue;
> +
> +	if (blk_queue_limit_bio_size(q))
> +		return blk_queue_get_max_sectors(q, bio_op(bio))
> +			<< SECTOR_SHIFT;
> +
> +	return UINT_MAX;
> +}

This patch adds an if-statement to the hot path and that may have a
slight negative performance impact. I recommend to follow the approach
of max_hw_sectors. That means removing QUEUE_FLAG_LIMIT_BIO_SIZE and to
initialize the maximum bio size to UINT_MAX in blk_set_default_limits().

Thanks,

Bart.