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Date: Tue, 7 Jan 2025 07:10:12 +0100
From: Christoph Hellwig <hch@lst.de>
To: John Garry <john.g.garry@oracle.com>
Cc: Christoph Hellwig <hch@lst.de>,
	Alexander Viro <viro@zeniv.linux.org.uk>,
	Christian Brauner <brauner@kernel.org>, Jan Kara <jack@suse.cz>,
	Chandan Babu R <chandan.babu@oracle.com>,
	"Darrick J. Wong" <djwong@kernel.org>,
	Hongbo Li <lihongbo22@huawei.com>,
	Ryusuke Konishi <konishi.ryusuke@gmail.com>,
	linux-nilfs@vger.kernel.org, linux-fsdevel@vger.kernel.org,
	linux-xfs@vger.kernel.org
Subject: Re: [PATCH 4/4] xfs: report the correct read/write dio alignment
 for reflinked inodes
Message-ID: <20250107061012.GA13898@lst.de>
References: <20250106151607.954940-1-hch@lst.de> <20250106151607.954940-5-hch@lst.de> <dd525ca1-68ff-4f6d-87a9-b0c67e592f83@oracle.com>
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On Mon, Jan 06, 2025 at 06:37:06PM +0000, John Garry wrote:
>> +	/*
>> +	 * On COW inodes we are forced to always rewrite an entire file system
>> +	 * block or RT extent.
>> +	 *
>> +	 * Because applications assume they can do sector sized direct writes
>> +	 * on XFS we fall back to buffered I/O for sub-block direct I/O in that
>> +	 * case.  Because that needs to copy the entire block into the buffer
>> +	 * cache it is highly inefficient and can easily lead to page cache
>> +	 * invalidation races.
>> +	 *
>> +	 * Tell applications to avoid this case by reporting the natively
>> +	 * supported direct I/O read alignment.
>
> Maybe I mis-read the complete comment, but did you really mean "natively 
> supported direct I/O write alignment"? You have been talking about writes 
> only, but then finally mention read alignment.

No, this is indeed intended to talk about the different (smaller) read
alignment we are now reporting.  But I guess the wording is confusing
enough that I should improve it?