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Date: Wed, 23 Apr 2025 07:44:20 +0200
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Luis Chamberlain <mcgrof@kernel.org>, Chris Mason <clm@fb.com>,
	Josef Bacik <josef@toxicpanda.com>, brauner@kernel.org,
	djwong@kernel.org, hch@lst.de, viro@zeniv.linux.org.uk,
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	catherine.hoang@oracle.com, linux-api@vger.kernel.org,
	Pankaj Raghav <p.raghav@samsung.com>,
	Daniel Gomez <da.gomez@samsung.com>
Subject: Re: [PATCH v7 11/14] xfs: add xfs_file_dio_write_atomic()
Message-ID: <20250423054420.GB23087@lst.de>
References: <20250415121425.4146847-1-john.g.garry@oracle.com> <20250415121425.4146847-12-john.g.garry@oracle.com> <aAa2HMvKcIGdbJlF@bombadil.infradead.org> <69302bf1-78b4-4b95-8e9b-df56dd1091c0@oracle.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

On Tue, Apr 22, 2025 at 07:08:32AM +0100, John Garry wrote:
> So consider userspace wants to write something atomically and we fail as a 
> HW-based atomic write is not possible. What is userspace going to do next?

Exactly.

>
> I heard something like "if HW-based atomics are not possible, then 
> something has not been configured properly for the FS" - that something 
> would be extent granularity and alignment, but we don't have a method to 
> ensure this. That is the whole point of having a FS fallback.

We now have the opt limit, right? (I'll review the reposted series
ASAP, but for now I'll assume it)  They can just tune their applications
to it, and trigger on a trace point for the fallback to monitor it.