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From:   Damien Le Moal <Damien.LeMoal@wdc.com>
To:     "javier.gonz@samsung.com" <javier@javigon.com>,
        Keith Busch <kbusch@kernel.org>
CC:     SelvaKumar S <selvakuma.s1@samsung.com>,
        "linux-nvme@lists.infradead.org" <linux-nvme@lists.infradead.org>,
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        "sagi@grimberg.me" <sagi@grimberg.me>,
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        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        "dm-devel@redhat.com" <dm-devel@redhat.com>,
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        "selvajove@gmail.com" <selvajove@gmail.com>,
        "nj.shetty@samsung.com" <nj.shetty@samsung.com>,
        "joshi.k@samsung.com" <joshi.k@samsung.com>,
        "Martin K . Petersen" <martin.petersen@oracle.com>
Subject: Re: [RFC PATCH v2 0/2] add simple copy support
Thread-Topic: [RFC PATCH v2 0/2] add simple copy support
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Date:   Mon, 7 Dec 2020 08:06:05 +0000
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On 2020/12/07 16:46, javier.gonz@samsung.com wrote:=0A=
> On 04.12.2020 23:40, Keith Busch wrote:=0A=
>> On Fri, Dec 04, 2020 at 11:25:12AM +0000, Damien Le Moal wrote:=0A=
>>> On 2020/12/04 20:02, SelvaKumar S wrote:=0A=
>>>> This patchset tries to add support for TP4065a ("Simple Copy Command")=
,=0A=
>>>> v2020.05.04 ("Ratified")=0A=
>>>>=0A=
>>>> The Specification can be found in following link.=0A=
>>>> https://nvmexpress.org/wp-content/uploads/NVM-Express-1.4-Ratified-TPs=
-1.zip=0A=
>>>>=0A=
>>>> This is an RFC. Looking forward for any feedbacks or other alternate=
=0A=
>>>> designs for plumbing simple copy to IO stack.=0A=
>>>>=0A=
>>>> Simple copy command is a copy offloading operation and is  used to cop=
y=0A=
>>>> multiple contiguous ranges (source_ranges) of LBA's to a single destin=
ation=0A=
>>>> LBA within the device reducing traffic between host and device.=0A=
>>>>=0A=
>>>> This implementation accepts destination, no of sources and arrays of=
=0A=
>>>> source ranges from application and attach it as payload to the bio and=
=0A=
>>>> submits to the device.=0A=
>>>>=0A=
>>>> Following limits are added to queue limits and are exposed in sysfs=0A=
>>>> to userspace=0A=
>>>> 	- *max_copy_sectors* limits the sum of all source_range length=0A=
>>>> 	- *max_copy_nr_ranges* limits the number of source ranges=0A=
>>>> 	- *max_copy_range_sectors* limit the maximum number of sectors=0A=
>>>> 		that can constitute a single source range.=0A=
>>>=0A=
>>> Same comment as before. I think this is a good start, but for this to b=
e really=0A=
>>> useful to users and kernel components alike, this really needs copy emu=
lation=0A=
>>> for drives that do not have a native copy feature, similarly to what wr=
ite zeros=0A=
>>> handling for instance: if the drive does not have a copy command (simpl=
e copy=0A=
>>> for NVMe or XCOPY for scsi), then the block layer should issue read/wri=
te=0A=
>>> commands to seamlessly execute the copy. Otherwise, this will only serv=
e a small=0A=
>>> niche for users and will not be optimal for FS and DM drivers that coul=
d be=0A=
>>> simplified with a generic block layer copy functionality.=0A=
>>>=0A=
>>> This is my 10 cents though, others may differ about this.=0A=
>>=0A=
>> Yes, I agree that copy emulation support should be included with the=0A=
>> hardware enabled solution.=0A=
> =0A=
> Keith, Damien,=0A=
> =0A=
> Can we do the block layer emulation with this patchset and then work in=
=0A=
> follow-up patchses on (i) the FS interface with F2FS as a first user and=
=0A=
> (ii) other HW accelerations such as XCOPY?=0A=
=0A=
The initial patchset supporting NVMe simple copy and emulation copy, all un=
der=0A=
an API that probably will be similar that of dm-kcopyd will cover all block=
=0A=
devices. Other hardware native support for copy functions such as scsi exte=
nded=0A=
copy can be added later under the hood without any API changes (or minimal =
changes).=0A=
=0A=
I am not sure what you mean by "FS interface for F2FS": the block layer API=
 for=0A=
this copy functionality will be what F2FS (and other FSes) will call. That =
is=0A=
the interface, no ?=0A=
=0A=
> For XCOPY, I believe we need to have a separate discussion as much works=
=0A=
> is already done that we should align to.=0A=
=0A=
I think Martin (added to this thread) and others have looked into it but I =
do=0A=
not think that anything made it into the kernel yet.=0A=
=0A=
=0A=
-- =0A=
Damien Le Moal=0A=
Western Digital Research=0A=