linux-kernel - Re: [PATCH v7 11/14] xfs: add xfs_file_dio_write

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Message-ID: <20250423054420.GB23087@lst.de>
Date: Wed, 23 Apr 2025 07:44:20 +0200
From: Christoph Hellwig <hch@....de>
To: John Garry <john.g.garry@...cle.com>
Cc: Luis Chamberlain <mcgrof@...nel.org>, Chris Mason <clm@...com>,
	Josef Bacik <josef@...icpanda.com>, brauner@...nel.org,
	djwong@...nel.org, hch@....de, viro@...iv.linux.org.uk,
	jack@...e.cz, cem@...nel.org, linux-fsdevel@...r.kernel.org,
	dchinner@...hat.com, linux-xfs@...r.kernel.org,
	linux-kernel@...r.kernel.org, ojaswin@...ux.ibm.com,
	ritesh.list@...il.com, martin.petersen@...cle.com,
	linux-ext4@...r.kernel.org, linux-block@...r.kernel.org,
	catherine.hoang@...cle.com, linux-api@...r.kernel.org,
	Pankaj Raghav <p.raghav@...sung.com>,
	Daniel Gomez <da.gomez@...sung.com>
Subject: Re: [PATCH v7 11/14] xfs: add xfs_file_dio_write_atomic()

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.