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From:   Nitesh Shetty <nitheshshetty@gmail.com>
Date:   Mon, 14 Aug 2023 22:25:54 +0530
Message-ID: <CAOSviJ1b5ySAugzKExa_ZQgOzvQAOWB3D-ZRMQeGmNpQbaoBSQ@mail.gmail.com>
Subject: Re: [dm-devel] [PATCH v14 00/11] Implement copy offload support
To:     Bart Van Assche <bvanassche@acm.org>
Cc:     Nitesh Shetty <nj.shetty@samsung.com>,
        Jens Axboe <axboe@kernel.dk>, Jonathan Corbet <corbet@lwn.net>,
        Alasdair Kergon <agk@redhat.com>,
        Mike Snitzer <snitzer@kernel.org>, dm-devel@redhat.com,
        Keith Busch <kbusch@kernel.org>,
        Christoph Hellwig <hch@lst.de>,
        Sagi Grimberg <sagi@grimberg.me>,
        Chaitanya Kulkarni <kch@nvidia.com>,
        Alexander Viro <viro@zeniv.linux.org.uk>,
        Christian Brauner <brauner@kernel.org>,
        martin.petersen@oracle.com, linux-doc@vger.kernel.org,
        gost.dev@samsung.com, linux-kernel@vger.kernel.org,
        linux-nvme@lists.infradead.org, linux-block@vger.kernel.org,
        mcgrof@kernel.org, dlemoal@kernel.org,
        linux-fsdevel@vger.kernel.org
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On Sat, Aug 12, 2023 at 3:42=E2=80=AFAM Bart Van Assche <bvanassche@acm.org=
> wrote:
>
> On 8/11/23 03:52, Nitesh Shetty wrote:
> > We achieve copy offload by sending 2 bio's with source and destination
> > info and merge them to form a request. This request is sent to driver.
> > So this design works only for request based storage drivers.
>
> [ ... ]
>
> > Overall series supports:
> > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=
=3D
> >       1. Driver
> >               - NVMe Copy command (single NS, TP 4065), including suppo=
rt
> >               in nvme-target (for block and file back end).
> >
> >       2. Block layer
> >               - Block-generic copy (REQ_OP_COPY_DST/SRC), operation wit=
h
> >                    interface accommodating two block-devs
> >                  - Merging copy requests in request layer
> >               - Emulation, for in-kernel user when offload is natively
> >                  absent
> >               - dm-linear support (for cases not requiring split)
> >
> >       3. User-interface
> >               - copy_file_range
>
> Is this sufficient? The combination of dm-crypt, dm-linear and the NVMe
> driver is very common. What is the plan for supporting dm-crypt?

Plan is to add offload support for other dm targets as part of subsequent
series once current patchset merges, dm targets can use emulation to
achieve the same at present.

> Shouldn't bio splitting be supported for dm-linear?
Handling split is tricky in this case, if we allow splitting, there is
no easy way
to match/merge different src/dst bio's. Once we have multi range support th=
en
we feel at least src bio's can be split. But this series split won't work.

Thank you,
Nitesh Shetty