Re: [PATCH 4/5] brd: split I/O at page boundaries

Yu Kuai
2025-04-29T01:38:34Z

Hi,

在 2025/04/29 2:07, Keith Busch 写道:
> On Mon, Apr 28, 2025 at 07:09:50AM -0700, Christoph Hellwig wrote:
>> A lot of complexity in brd stems from the fact that it tries to handle
>> I/O spanning two backing pages. Instead limit the size of a single
>> bvec iteration so that it never crosses a page boundary and remove all
>> the now unneeded code.
>
> Doesn't bio_for_each_segment() already limit bvecs on page boundaries?
> You'd need to use bio_for_each_bvec() to get multi-page bvecs.

I think it only limit bvecs on page boundaries on the issue side, not
disk side.

For example, if user issue an IO (2k + 4k), will bio_for_each_segment()
split this IO into (2k + 2k) and (4k + 2k), I do not test yet, but I
think the answer is no.

Thanks,
Kuai

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