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To:     Max Gurtovoy <mgurtovoy@nvidia.com>,
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Subject: Re: [RFC PATCH v5 0/4] add simple copy support
Thread-Topic: [RFC PATCH v5 0/4] add simple copy support
Thread-Index: AQHXByxPYjd3lKFugEyHev6iOAHEsg==
Date:   Sat, 10 Apr 2021 00:29:59 +0000
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On 4/9/21 17:22, Max Gurtovoy wrote:=0A=
> On 2/19/2021 2:45 PM, 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=
>> Simple copy command is a copy offloading operation and is  used to copy=
=0A=
>> multiple contiguous ranges (source_ranges) of LBA's to a single destinat=
ion=0A=
>> LBA within the device reducing traffic between host and device.=0A=
>>=0A=
>> This implementation doesn't add native copy offload support for stacked=
=0A=
>> devices rather copy offload is done through emulation. Possible use=0A=
>> cases are F2FS gc and BTRFS relocation/balance.=0A=
>>=0A=
>> *blkdev_issue_copy* takes source bdev, no of sources, array of source=0A=
>> ranges (in sectors), destination bdev and destination offset(in sectors)=
.=0A=
>> If both source and destination block devices are same and copy_offload =
=3D 1,=0A=
>> then copy is done through native copy offloading. Copy emulation is used=
=0A=
>> in other cases.=0A=
>>=0A=
>> As SCSI XCOPY can take two different block devices and no of source rang=
e is=0A=
>> equal to 1, this interface can be extended in future to support SCSI XCO=
PY.=0A=
> Any idea why this TP wasn't designed for copy offload between 2 =0A=
> different namespaces in the same controller ?=0A=
=0A=
Yes, it was the first attempt so to keep it simple.=0A=
=0A=
Further work is needed to add incremental TP so that we can also do a copy=
=0A=
between the name-spaces of same controller (if we can't already) and to the=
=0A=
namespaces that belongs to the different controller.=0A=
=0A=
> And a simple copy will be the case where the src_nsid =3D=3D dst_nsid ?=
=0A=
>=0A=
> Also why there are multiple source ranges and only one dst range ? We =0A=
> could add a bit to indicate if this range is src or dst..=0A=
>=0A=
>=0A=
=0A=
=0A=
=0A=