linux-kernel - Re: [PATCH v20 09/12] dm: Add support for copy offload

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Date: Tue, 21 May 2024 19:38:50 +0530
From: Nitesh Shetty <nj.shetty@...sung.com>
To: Hannes Reinecke <hare@...e.de>
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,
	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 09/12] dm: Add support for copy offload

On 21/05/24 09:11AM, Hannes Reinecke wrote:
>On 5/20/24 12:20, Nitesh Shetty wrote:
>>Before enabling copy for dm target, check if underlying devices and
>>dm target support copy. Avoid split happening inside dm target.
>>Fail early if the request needs split, currently splitting copy
>>request is not supported.
>>
>>Signed-off-by: Nitesh Shetty <nj.shetty@...sung.com>
>>---
>>@@ -397,6 +397,9 @@ struct dm_target {
>>  	 * bio_set_dev(). NOTE: ideally a target should _not_ need this.
>>  	 */
>>  	bool needs_bio_set_dev:1;
>>+
>>+	/* copy offload is supported */
>>+	bool copy_offload_supported:1;
>>  };
>>  void *dm_per_bio_data(struct bio *bio, size_t data_size);
>
>Errm. Not sure this will work. DM tables might be arbitrarily, 
>requiring us to _split_ the copy offload request according to the 
>underlying component devices. But we explicitly disallowed a split in 
>one of the earlier patches.
>Or am I wrong?
>
Yes you are right w.r.to split, we disallow split.
But this flag indicates whether we support copy offload in dm-target or
not. At present we support copy offload only in dm-linear.
For other dm-target, eventhough underlaying device supports copy
offload, dm-target based on it wont support copy offload.
If the present series get merged, we can test and integrate more
targets.

Regards,
Nitesh Shetty