linux-kernel - Re: [RFC PATCH v5 0/4] add simple copy support

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Message-ID: <20210220191921.GA7968@redsun51.ssa.fujisawa.hgst.com>
Date:   Sun, 21 Feb 2021 04:19:21 +0900
From:   Keith Busch <kbusch@...nel.org>
To:     David Laight <David.Laight@...lab.com>
Cc:     'SelvaKumar S' <selvakuma.s1@...sung.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "damien.lemoal@....com" <damien.lemoal@....com>,
        "hch@....de" <hch@....de>, "sagi@...mberg.me" <sagi@...mberg.me>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "selvajove@...il.com" <selvajove@...il.com>,
        "joshiiitr@...il.com" <joshiiitr@...il.com>,
        "nj.shetty@...sung.com" <nj.shetty@...sung.com>,
        "joshi.k@...sung.com" <joshi.k@...sung.com>,
        "javier.gonz@...sung.com" <javier.gonz@...sung.com>,
        "kch@...nel.org" <kch@...nel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>
Subject: Re: [RFC PATCH v5 0/4] add simple copy support

On Sat, Feb 20, 2021 at 06:01:56PM +0000, David Laight wrote:
> From: SelvaKumar S
> > Sent: 19 February 2021 12:45
> > 
> > This patchset tries to add support for TP4065a ("Simple Copy Command"),
> > v2020.05.04 ("Ratified")
> > 
> > The Specification can be found in following link.
> > https://nvmexpress.org/wp-content/uploads/NVM-Express-1.4-Ratified-TPs-1.zip
> > 
> > Simple copy command is a copy offloading operation and is  used to copy
> > multiple contiguous ranges (source_ranges) of LBA's to a single destination
> > LBA within the device reducing traffic between host and device.
> 
> Sounds to me like the real reason is that the copy just ends up changing
> some indirect block pointers rather than having to actually copy the data.

I guess an implementation could do that, but I think that's missing the
point of the command. The intention is to copy the data to a new
location on the media for host managed garbage collection.