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Date: Tue, 26 Aug 2025 10:02:00 +0200
From: Christoph Hellwig <hch@lst.de>
To: Keith Busch <kbusch@kernel.org>
Cc: Keith Busch <kbusch@meta.com>, linux-block@vger.kernel.org,
	linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
	snitzer@kernel.org, axboe@kernel.dk, dw@davidwei.uk,
	brauner@kernel.org, martin.petersen@oracle.com, djwong@kernel.org,
	linux-xfs@vger.kernel.org, viro@zeniv.linux.org.uk
Subject: Re: [PATCHv3 3/8] block: align the bio after building it
Message-ID: <20250826080200.GA23095@lst.de>
References: <20250819164922.640964-1-kbusch@meta.com> <20250819164922.640964-4-kbusch@meta.com> <20250825074744.GF20853@lst.de> <aK0Bsf6AKL8a0wFy@kbusch-mbp>
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On Mon, Aug 25, 2025 at 06:37:05PM -0600, Keith Busch wrote:
> On Mon, Aug 25, 2025 at 09:47:44AM +0200, Christoph Hellwig wrote:
> > Also with this we should be able to drop the iov_iter_alignment check
> > for always COW inodes in xfs_file_dio_write.  If you don't feel like
> > doing that yourself I can add it to my todo list.
> 
> I'm unsure about the commit that introduced that behavior, so I think
> you should remove it if you know its okay. :)

Yeah.

> Specifically, we have this in the comments and commit message:
> 
>   check the alignment of each individual iovec segment, as they could
>   end up with different I/Os due to the way bio_iov_iter_get_pages works 
> 
> bio_iov_iter_get_pages() might submit the segments as separate IO's
> anyway for other reasons. I am not sure why the alignment conditions are
> handled specifically here.

I'll take another look.  Basically what this wants to prevent is
bio_iov_iter_get_pages creating bios not aligned to file system
block size.