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Date: Sat, 1 Jun 2024 07:47:01 +0200
From: Christoph Hellwig <hch@lst.de>
To: Nitesh Shetty <nj.shetty@samsung.com>
Cc: Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
	Alasdair Kergon <agk@redhat.com>, Mike Snitzer <snitzer@kernel.org>,
	Mikulas Patocka <mpatocka@redhat.com>,
	Keith Busch <kbusch@kernel.org>, Christoph Hellwig <hch@lst.de>,
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	dm-devel@lists.linux.dev, linux-nvme@lists.infradead.org,
	linux-fsdevel@vger.kernel.org
Subject: Re: [PATCH v20 00/12] Implement copy offload support
Message-ID: <20240601054701.GA5613@lst.de>
References: <CGME20240520102747epcas5p33497a911ca70c991e5da8e22c5d1336b@epcas5p3.samsung.com> <20240520102033.9361-1-nj.shetty@samsung.com>
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On Mon, May 20, 2024 at 03:50:13PM +0530, Nitesh Shetty wrote:
> So copy offload works only for request based storage drivers.

I don't think that is actually true.  It just requires a fair amount of
code in a bio based driver to match the bios up.

I'm missing any kind of information on what this patch set as-is
actually helps with.  What operations are sped up, for what operations
does it reduce resource usage?

Part of that might be that the included use case of offloading
copy_file_range doesn't seem particularly useful - on any advance
file system that would be done using reflinks anyway.

Have you considered hooking into dm-kcopyd which would be an
instant win instead?  Or into garbage collection in zoned or other
log structured file systems?  Those would probably really like
multiple source bios, though.