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Date: Thu, 20 Mar 2025 15:12:00 +0100
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>, alx@kernel.org, brauner@kernel.org,
	djwong@kernel.org, dchinner@redhat.com, linux-man@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-xfs@vger.kernel.org,
	linux-kernel@vger.kernel.org, ojaswin@linux.ibm.com,
	ritesh.list@gmail.com, martin.petersen@oracle.com
Subject: Re: [PATCH RFC] statx.2: Add stx_atomic_write_unit_max_opt
Message-ID: <20250320141200.GC10939@lst.de>
References: <20250319114402.3757248-1-john.g.garry@oracle.com> <20250320070048.GA14099@lst.de> <c656fa4d-eb76-4caa-8a71-a8d8a2ba6206@oracle.com>
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On Thu, Mar 20, 2025 at 09:19:40AM +0000, John Garry wrote:
> But is there value in reporting this limit? I am not sure. I am not sure 
> what the user would do with this info.

Align their data structures to it, e.g. size the log buffers to it.

> Maybe, for example, they want to write 1K consecutive 16K pages, each 
> atomically, and decide to do a big 16M atomic write but find that it is 
> slow as bdev atomic limit is < 16M.
>
> Maybe I should just update the documentation to mention that for XFS they 
> should check the mounted bdev atomic limits.

For something working on files having to figure out the underlying
block device (which is non-trivial given the various methods of
multi-device support) and then looking into block sysfs is a no-go.

So if we have any sort of use case for it we should expose the limit.