linux-kernel - Re: [PATCH v20 00/12] Implement copy offload support

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Date: Sat, 1 Jun 2024 07:47:01 +0200
From: Christoph Hellwig <hch@....de>
To: Nitesh Shetty <nj.shetty@...sung.com>
Cc: Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
	Alasdair Kergon <agk@...hat.com>, Mike Snitzer <snitzer@...nel.org>,
	Mikulas Patocka <mpatocka@...hat.com>,
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>,
	Chaitanya Kulkarni <kch@...dia.com>,
	Alexander Viro <viro@...iv.linux.org.uk>,
	Christian Brauner <brauner@...nel.org>, Jan Kara <jack@...e.cz>,
	martin.petersen@...cle.com, bvanassche@....org, david@...morbit.com,
	hare@...e.de, damien.lemoal@...nsource.wdc.com,
	anuj20.g@...sung.com, joshi.k@...sung.com, nitheshshetty@...il.com,
	gost.dev@...sung.com, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
	dm-devel@...ts.linux.dev, linux-nvme@...ts.infradead.org,
	linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v20 00/12] Implement copy offload support

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.