linux-kernel - Re: [PATCH v8 05/10] block: Add core atomic write support

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Date: Wed, 19 Jun 2024 08:59:33 +0100
From: John Garry <john.g.garry@...cle.com>
To: Keith Busch <kbusch@...nel.org>
Cc: Christoph Hellwig <hch@....de>, axboe@...nel.dk, sagi@...mberg.me,
        jejb@...ux.ibm.com, martin.petersen@...cle.com,
        viro@...iv.linux.org.uk, brauner@...nel.org, dchinner@...hat.com,
        jack@...e.cz, djwong@...nel.org, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, tytso@....edu, jbongio@...gle.com,
        linux-scsi@...r.kernel.org, ojaswin@...ux.ibm.com, linux-aio@...ck.org,
        linux-btrfs@...r.kernel.org, io-uring@...r.kernel.org,
        nilay@...ux.ibm.com, ritesh.list@...il.com, willy@...radead.org,
        agk@...hat.com, snitzer@...nel.org, mpatocka@...hat.com,
        dm-devel@...ts.linux.dev, hare@...e.de,
        Himanshu Madhani <himanshu.madhani@...cle.com>
Subject: Re: [PATCH v8 05/10] block: Add core atomic write support

On 18/06/2024 18:25, Keith Busch wrote:
> On Tue, Jun 18, 2024 at 08:46:31AM +0100, John Garry wrote:
>> About NVMe, the spec says that NABSN and NOIOB may not be related to one
>> another (command set spec 1.0d 5.8.2.1), but I am wondering if people really
>> build HW which would have different NABSN/NABSPF and NOIOB. I don't know.
> The history of NOIOB is from an nvme drive that had two back-end
> controllers with their own isolated storage, and then striped together
> on the front end for the host to see. A command crossing the stripe
> boundary takes a slow path to split it for each backend controller's
> portion and merge the results. Subsequent implementations may have
> different reasons for advertising this boundary, but that was the
> original.

In this case, I would expect NOIOB >= atomic write boundary.

Would it be sane to have a NOIOB < atomic write boundary in some other 
config?

I can support these possibilities, but the code will just get more complex.

> 
> Anyway, there was an idea that the stripe size could be user
> configurable, though that never shipped as far as I know. If it had,
> then the optimal NOIOB could be made larger, but the atomic write size
> doesn't change.

Thanks,
John