linux-kernel - Re: [PATCH v4 00/10] Add Copy offload support

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Message-ID: <46e95412-9a79-51f8-3d52-caed4875d41f@opensource.wdc.com>
Date:   Mon, 2 May 2022 21:54:55 +0900
From:   Damien Le Moal <damien.lemoal@...nsource.wdc.com>
To:     Dave Chinner <david@...morbit.com>,
        Nitesh Shetty <nj.shetty@...sung.com>
Cc:     linux-block@...r.kernel.org, linux-scsi@...r.kernel.org,
        dm-devel@...hat.com, linux-nvme@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, nitheshshetty@...il.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 00/10] Add Copy offload support

On 2022/05/02 13:09, Dave Chinner wrote:
> On Wed, Apr 27, 2022 at 06:19:51PM +0530, Nitesh Shetty wrote:
>> O Wed, Apr 27, 2022 at 11:19:48AM +0900, Damien Le Moal wrote:
>>> On 4/26/22 19:12, Nitesh Shetty wrote:
>>>> The patch series covers the points discussed in November 2021 virtual call
>>>> [LSF/MM/BFP TOPIC] Storage: Copy Offload[0].
>>>> We have covered the Initial agreed requirements in this patchset.
>>>> Patchset borrows Mikulas's token based approach for 2 bdev
>>>> implementation.
>>>>
>>>> Overall series supports –
>>>>
>>>> 1. Driver
>>>> - NVMe Copy command (single NS), including support in nvme-target (for
>>>>     block and file backend)
>>>
>>> It would also be nice to have copy offload emulation in null_blk for testing.
>>>
>>
>> We can plan this in next phase of copy support, once this series settles down.
> 
> Why not just hook the loopback driver up to copy_file_range() so
> that the backend filesystem can just reflink copy the ranges being
> passed? That would enable testing on btrfs, XFS and NFSv4.2 hosted
> image files without needing any special block device setup at all...

That is a very good idea ! But that will cover only the non-zoned case. For copy
offload on zoned devices, adding support in null_blk is probably the simplest
thing to do.

> 
> i.e. I think you're doing this compeltely backwards by trying to
> target non-existent hardware first....
> 
> Cheers,
> 
> Dave.


-- 
Damien Le Moal
Western Digital Research