linux-kernel - Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed atomically

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Date: Mon, 29 Jan 2024 07:20:35 +0100
From: Christoph Hellwig <hch@....de>
To: John Garry <john.g.garry@...cle.com>
Cc: Keith Busch <kbusch@...nel.org>, axboe@...nel.dk, hch@....de,
	sagi@...mberg.me, jejb@...ux.ibm.com, martin.petersen@...cle.com,
	djwong@...nel.org, viro@...iv.linux.org.uk, brauner@...nel.org,
	dchinner@...hat.com, jack@...e.cz, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	linux-xfs@...r.kernel.org, linux-fsdevel@...r.kernel.org,
	tytso@....edu, jbongio@...gle.com, linux-scsi@...r.kernel.org,
	ming.lei@...hat.com, ojaswin@...ux.ibm.com, bvanassche@....org,
	Alan Adamson <alan.adamson@...cle.com>
Subject: Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed
 atomically

On Thu, Jan 25, 2024 at 11:28:22AM +0000, John Garry wrote:
> We have limits checks in XFS iomap and fops.c, but we would also want to 
> ensure that the the block layer is not doing anything it shouldn't be doing 
> after submit_bio_noacct(), like merging atomic write BIOs which straddle a 
> boundary or exceed atomic_max (if there were any merging).
>
> The SCSI standard already has provision for error'ing an atomic write 
> command which exceeds the target atomic write capabilities, while NVMe 
> doesn't.

Can you get Oracle to propose this for NVMe?  It always helps if these
suggestions come from a large buyer of NVMe equipment.

> BTW, Christoph did mention that he would like to see this:
> https://lore.kernel.org/linux-nvme/20231109153603.GA2188@lst.de/

I can probably live with a sufficiently low-level block layer check.