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

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Date:   Sat, 10 Apr 2021 00:29:59 +0000
From:   Chaitanya Kulkarni <Chaitanya.Kulkarni@....com>
To:     Max Gurtovoy <mgurtovoy@...dia.com>,
        SelvaKumar S <selvakuma.s1@...sung.com>,
        "linux-nvme@...ts.infradead.org" <linux-nvme@...ts.infradead.org>
CC:     "axboe@...nel.dk" <axboe@...nel.dk>,
        Damien Le Moal <Damien.LeMoal@....com>,
        "kch@...nel.org" <kch@...nel.org>,
        "sagi@...mberg.me" <sagi@...mberg.me>,
        "snitzer@...hat.com" <snitzer@...hat.com>,
        "selvajove@...il.com" <selvajove@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nj.shetty@...sung.com" <nj.shetty@...sung.com>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-fsdevel@...r.kernel.org" <linux-fsdevel@...r.kernel.org>,
        "dm-devel@...hat.com" <dm-devel@...hat.com>,
        "joshi.k@...sung.com" <joshi.k@...sung.com>,
        "javier.gonz@...sung.com" <javier.gonz@...sung.com>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "joshiiitr@...il.com" <joshiiitr@...il.com>,
        "hch@....de" <hch@....de>
Subject: Re: [RFC PATCH v5 0/4] add simple copy support

On 4/9/21 17:22, Max Gurtovoy wrote:
> On 2/19/2021 2:45 PM, SelvaKumar S wrote:
>> 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.
>>
>> This implementation doesn't add native copy offload support for stacked
>> devices rather copy offload is done through emulation. Possible use
>> cases are F2FS gc and BTRFS relocation/balance.
>>
>> *blkdev_issue_copy* takes source bdev, no of sources, array of source
>> ranges (in sectors), destination bdev and destination offset(in sectors).
>> If both source and destination block devices are same and copy_offload = 1,
>> then copy is done through native copy offloading. Copy emulation is used
>> in other cases.
>>
>> As SCSI XCOPY can take two different block devices and no of source range is
>> equal to 1, this interface can be extended in future to support SCSI XCOPY.
> Any idea why this TP wasn't designed for copy offload between 2 
> different namespaces in the same controller ?

Yes, it was the first attempt so to keep it simple.

Further work is needed to add incremental TP so that we can also do a copy
between the name-spaces of same controller (if we can't already) and to the
namespaces that belongs to the different controller.

> And a simple copy will be the case where the src_nsid == dst_nsid ?
>
> Also why there are multiple source ranges and only one dst range ? We 
> could add a bit to indicate if this range is src or dst..
>
>