linux-kernel - Re: [PATCH v15 03/12] block: add copy offload support

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Date:   Thu, 7 Sep 2023 12:46:11 +0530
From:   Nitesh Shetty <nj.shetty@...sung.com>
To:     Hannes Reinecke <hare@...e.de>
Cc:     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>,
        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 03/12] block: add copy offload support

On 07/09/23 07:49AM, Hannes Reinecke wrote:
>On 9/6/23 18:38, Nitesh Shetty wrote:
>
>Hmm. That looks a bit odd. Why do you have to use wait_for_completion?

wait_for_completion is waiting for all the copy IOs to complete,
when caller does not pass endio handler.
Copy IO submissions are still async, as in previous revisions.

>Can't you submit the 'src' bio, and then submit the 'dst' bio from the 
>endio handler of the 'src' bio?
We can't do this with the current bio merging approach.
'src' bio waits for the 'dst' bio to arrive in request layer.
Note that both bio's should be present in request reaching the driver,
to form the copy-cmd.

Thank You,
Nitesh Shetty