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Message-ID: <ff43517e-ad30-4608-a8ec-401108129ea5@oracle.com>
Date:   Mon, 4 Dec 2023 09:35:18 +0000
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Subject: Re: [PATCH 02/21] block: Limit atomic writes according to bio and
 queue limits
Content-Language: en-US
To:     Ming Lei <ming.lei@redhat.com>
Cc:     axboe@kernel.dk, kbusch@kernel.org, hch@lst.de, sagi@grimberg.me,
        jejb@linux.ibm.com, martin.petersen@oracle.com, djwong@kernel.org,
        viro@zeniv.linux.org.uk, brauner@kernel.org,
        chandan.babu@oracle.com, dchinner@redhat.com,
        linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-xfs@vger.kernel.org,
        linux-fsdevel@vger.kernel.org, tytso@mit.edu, jbongio@google.com,
        linux-api@vger.kernel.org
References: <20230929102726.2985188-1-john.g.garry@oracle.com>
 <20230929102726.2985188-3-john.g.garry@oracle.com> <ZW1FOFWsUGUNLajE@fedora>
 <ZW1NxiEh2x82SOai@fedora>
From:   John Garry <john.g.garry@oracle.com>
Organization: Oracle Corporation
In-Reply-To: <ZW1NxiEh2x82SOai@fedora>
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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