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Date: Mon, 29 Jan 2024 07:20:35 +0100
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Keith Busch <kbusch@kernel.org>, axboe@kernel.dk, 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,
	dchinner@redhat.com, jack@suse.cz, 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-scsi@vger.kernel.org,
	ming.lei@redhat.com, ojaswin@linux.ibm.com, bvanassche@acm.org,
	Alan Adamson <alan.adamson@oracle.com>
Subject: Re: [PATCH v3 15/15] nvme: Ensure atomic writes will be executed
 atomically
Message-ID: <20240129062035.GB19796@lst.de>
References: <20240124113841.31824-1-john.g.garry@oracle.com> <20240124113841.31824-16-john.g.garry@oracle.com> <ZbGwv4uFdJyfKtk5@kbusch-mbp.dhcp.thefacebook.com> <dbb3ad13-7524-4861-8006-b2ea426fbacd@oracle.com>
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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.