linux-kernel - Re: [PATCH] block: fix unexpected split in bio_discard

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Message-Id: <B7093938-9D67-4987-8B6B-B05890147580@smartx.com>
Date:   Mon, 21 Aug 2023 13:22:48 +0800
From:   Li Feng <fengli@...rtx.com>
To:     Jens Axboe <axboe@...nel.dk>,
        "open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] block: fix unexpected split in bio_discard_limit

Ping…

Thanks,
Li

> 2023年8月17日 下午3:55，Li Feng <fengli@...rtx.com> 写道：
> 
> bio_discard_limit() enforces discard boundaries within the range of 32-bit
> unsigned integers, resulting in unexpected discard cut boundaries.
> 
> For example, max discard size = 1MiB, discard_granularity = 512B, then the
> discard lengths sent in the range [0,4G) are 1MiB, 1MiB... (1MiB-512).
> The next discard offset from 4G is [4G-512, 4G-512+1MiB).
> The discard of the 4G offset boundary does not comply with the optimal 1MiB
> size.
> 
> Signed-off-by: Li Feng <fengli@...rtx.com>
> ---
> block/blk-lib.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/block/blk-lib.c b/block/blk-lib.c
> index e59c3069e835..ec95508c3593 100644
> --- a/block/blk-lib.c
> +++ b/block/blk-lib.c
> @@ -32,7 +32,7 @@ static sector_t bio_discard_limit(struct block_device *bdev, sector_t sector)
> 	 * Align the bio size to the discard granularity to make splitting the bio
> 	 * at discard granularity boundaries easier in the driver if needed.
> 	 */
> -	return round_down(UINT_MAX, discard_granularity) >> SECTOR_SHIFT;
> +	return round_down(ULONG_MAX, discard_granularity) >> SECTOR_SHIFT;
> }
> 
> int __blkdev_issue_discard(struct block_device *bdev, sector_t sector,
> -- 
> 2.41.0
>