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Date: Thu, 21 Dec 2023 12:48:24 +0000
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Subject: Re: [PATCH v2 00/16] block atomic writes
To: Christoph Hellwig <hch@lst.de>
Cc: "Darrick J. Wong" <djwong@kernel.org>, axboe@kernel.dk, kbusch@kernel.org,
        sagi@grimberg.me, jejb@linux.ibm.com, martin.petersen@oracle.com,
        viro@zeniv.linux.org.uk, brauner@kernel.org, dchinner@redhat.com,
        jack@suse.cz, linux-block@vger.kernel.org,
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        ming.lei@redhat.com, jaswin@linux.ibm.com, bvanassche@acm.org
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On 21/12/2023 12:19, Christoph Hellwig wrote:
>> So then we could have:
>> - ubuf / iovecs need to be PAGE-aligned
>> - each iovec needs to be length of multiple of atomic_write_unit_min. If
>> total length > PAGE_SIZE, each iovec also needs to be a multiple of
>> PAGE_SIZE.
>>
>> I'd rather something simpler. Maybe it's ok.
> If we decided to not support atomic writes on anything setting a virt
> boundary we don't have to care about the alignment of each vector,

ok, I think that alignment is not so important, but we still need to 
consider a minimum length per iovec, such that we will always be able to 
fit a write of length atomic_write_unit_max in a bio.

> and IMHO we should do that as everything else would be a life in
> constant pain.  If we really have a use case for atomic writes on
> consumer NVMe devices we'll just have to limit it to a single iovec.

I'd be more inclined to say that SGL support is compulsory, but I don't 
know if that is limiting atomic writes support to an unsatisfactory 
market segment.