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

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Date:   Tue, 22 Aug 2023 21:27:57 +0800
From:   Li Feng <fengli@...rtx.com>
To:     Ming Lei <ming.lei@...hat.com>
Cc:     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



> 2023年8月22日 21:07，Ming Lei <ming.lei@...hat.com> 写道：
> 
> 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,
> 
Got it, many thanks.