linux-kernel - Re: [PATCH v15 02/12] Add infrastructure for copy offload in block and request layer.

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Message-ID: <d2c3a257-0505-4d3e-ae71-28015952cef6@suse.de>
Date:   Thu, 7 Sep 2023 07:39:14 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Nitesh Shetty <nj.shetty@...sung.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>,
        Chaitanya Kulkarni <kch@...dia.com>,
        Alexander Viro <viro@...iv.linux.org.uk>,
        Christian Brauner <brauner@...nel.org>
Cc:     martin.petersen@...cle.com, mcgrof@...nel.org,
        gost.dev@...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 v15 02/12] Add infrastructure for copy offload in block
 and request layer.

On 9/6/23 18:38, Nitesh Shetty wrote:
> We add two new opcode REQ_OP_COPY_SRC, REQ_OP_COPY_DST.
> Since copy is a composite operation involving src and dst sectors/lba,
> each needs to be represented by a separate bio to make it compatible
> with device mapper.
> We expect caller to take a plug and send bio with source information,
> followed by bio with destination information.
> Once the src bio arrives we form a request and wait for destination
> bio. Upon arrival of destination we merge these two bio's and send
> corresponding request down to device driver.
> 
> Signed-off-by: Nitesh Shetty <nj.shetty@...sung.com>
> Signed-off-by: Anuj Gupta <anuj20.g@...sung.com>
> ---
>   block/blk-core.c          |  7 +++++++
>   block/blk-merge.c         | 41 +++++++++++++++++++++++++++++++++++++++
>   block/blk.h               | 16 +++++++++++++++
>   block/elevator.h          |  1 +
>   include/linux/bio.h       |  6 +-----
>   include/linux/blk_types.h | 10 ++++++++++
>   6 files changed, 76 insertions(+), 5 deletions(-)
> 
Having two separate bios is okay, and what one would expect.
What is slightly strange is the merging functionality;
That could do with some more explanation why this approach was taken.
And also some checks in the merging code to avoid merging non-copy 
offload  bios.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                Kernel Storage Architect
hare@...e.de                              +49 911 74053 688
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