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

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Message-ID: <393edf87-30c9-48b8-b703-4b8e514ac4d9@suse.de>
Date: Tue, 4 Jun 2024 09:16:36 +0200
From: Hannes Reinecke <hare@...e.de>
To: Christoph Hellwig <hch@....de>, 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>,
 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 00/12] Implement copy offload support

On 6/4/24 06:32, Christoph Hellwig wrote:
> On Mon, Jun 03, 2024 at 10:53:39AM +0000, Nitesh Shetty wrote:
>> The major benefit of this copy-offload/emulation framework is
>> observed in fabrics setup, for copy workloads across the network.
>> The host will send offload command over the network and actual copy
>> can be achieved using emulation on the target (hence patch 4).
>> This results in higher performance and lower network consumption,
>> as compared to read and write travelling across the network.
>> With this design of copy-offload/emulation we are able to see the
>> following improvements as compared to userspace read + write on a
>> NVMeOF TCP setup:
> 
> What is the use case of this?   What workloads does raw copies a lot
> of data inside a single block device?
> 

The canonical example would be VM provisioning from a master copy.
That's not within a single block device, mind; that's more for copying 
the contents of one device to another.
But I wasn't aware that this approach is limited to copying within a 
single block devices; that would be quite pointless indeed.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich