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

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Date:   Tue, 22 Aug 2023 21:07:56 +0800
From:   Ming Lei <ming.lei@...hat.com>
To:     Li Feng <fengli@...rtx.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        "open list:BLOCK LAYER" <linux-block@...r.kernel.org>,
        open list <linux-kernel@...r.kernel.org>, lifeng1519@...il.com,
        Ming Lei <ming.lei@...hat.com>
Subject: Re: [PATCH] block: fix unexpected split in bio_discard_limit

On Thu, Aug 17, 2023 at 3:42 PM Li Feng <fengli@...rtx.com> wrote:
>
> bio_discard_limit() enforces discard boundaries within the range of 32-bit
> unsigned integers, resulting in unexpected discard cut boundaries.

Any bio size can't be bigger than UINT_MAX, see bio definition.

>
> 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.

As mentioned, max bio size is 4GB, so there shouldn't be such issue.

Thanks,