Re: [PATCH 02/21] block: Limit atomic writes according to bio and queue limits

John Garry
2023-12-04T09:48:26Z

On 04/12/2023 03:55, Ming Lei wrote:

Hi Ming,

> On Mon, Dec 04, 2023 at 11:19:20AM +0800, Ming Lei wrote:
>> On Fri, Sep 29, 2023 at 10:27:07AM +0000, John Garry wrote:
>>> We rely the block layer always being able to send a bio of size
>>> atomic_write_unit_max without being required to split it due to request
>>> queue or other bio limits.
>>>
>>> A bio may contain min(BIO_MAX_VECS, limits->max_segments) vectors,
>>> and each vector is at worst case the device logical block size from
>>> direct IO alignment requirement.
>> Both unit_max and unit_min are applied to FS bio, which is built over
>> single userspace buffer, so only the 1st and last vector can include
> Actually it isn't true for pwritev, and sorry for the noise.

Yeah, I think that it should be:

(max_segments - 2) * PAGE_SIZE

And we need to enforce that any middle vectors are PAGE-aligned.

Thanks,
John