linux-kernel - Re: [PATCH v12 5/9] nvme: add copy offload support

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Date:   Mon, 10 Jul 2023 11:44:01 +0530
From:   Nitesh Shetty <nj.shetty@...sung.com>
To:     Christoph Hellwig <hch@...radead.org>
Cc:     "Martin K. Petersen" <martin.petersen@...cle.com>,
        Jens Axboe <axboe@...nel.dk>, Jonathan Corbet <corbet@....net>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...nel.org>, dm-devel@...hat.com,
        Keith Busch <kbusch@...nel.org>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        James Smart <james.smart@...adcom.com>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>,
        linux-scsi@...r.kernel.org, willy@...radead.org, hare@...e.de,
        djwong@...nel.org, bvanassche@....org, ming.lei@...hat.com,
        dlemoal@...nel.org, nitheshshetty@...il.com, gost.dev@...sung.com,
        Kanchan Joshi <joshi.k@...sung.com>,
        Javier González <javier.gonz@...sung.com>,
        Anuj Gupta <anuj20.g@...sung.com>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        linux-nvme@...ts.infradead.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v12 5/9] nvme: add copy offload support

On 23/06/08 09:24PM, Christoph Hellwig wrote:
>On Thu, Jun 08, 2023 at 05:38:17PM +0530, Nitesh Shetty wrote:
>> Sure, we can do away with subsys and realign more on single namespace copy.
>> We are planning to use token to store source info, such as src sector,
>> len and namespace. Something like below,
>>
>> struct nvme_copy_token {
>> 	struct nvme_ns *ns; // to make sure we are copying within same namespace
>> /* store source info during *IN operation, will be used by *OUT operation */
>> 	sector_t src_sector;
>> 	sector_t sectors;
>> };
>> Do you have any better way to handle this in mind ?
>
>In general every time we tried to come up with a request payload that is
>not just data passed to the device it has been a nightmare.
>
>So my gut feeling would be that bi_sector and bi_iter.bi_size are the
>ranges, with multiple bios being allowed to form the input data, similar
>to how we implement discard merging.
>
>The interesting part is how we'd match up these bios.  One idea would
>be that since copy by definition doesn't need integrity data we just
>add a copy_id that unions it, and use a simple per-gendisk copy I/D
>allocator, but I'm not entirely sure how well that interacts stacking
>drivers.

V13[1] implements that route. Please see if that matches with what you had
in mind?

[1] https://lore.kernel.org/linux-nvme/20230627183629.26571-1-nj.shetty@samsung.com/

Thank you, 
Nitesh Shetty