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Subject: Re: [PATCH v3 4/4] io_uring: add support for zone-append
To:     Kanchan Joshi <joshi.k@samsung.com>, viro@zeniv.linux.org.uk,
        bcrl@kvack.org
Cc:     hch@infradead.org, Damien.LeMoal@wdc.com, asml.silence@gmail.com,
        linux-fsdevel@vger.kernel.org, mb@lightnvm.io,
        linux-kernel@vger.kernel.org, linux-aio@kvack.org,
        io-uring@vger.kernel.org, linux-block@vger.kernel.org,
        Selvakumar S <selvakuma.s1@samsung.com>,
        Nitesh Shetty <nj.shetty@samsung.com>,
        Javier Gonzalez <javier.gonz@samsung.com>
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From:   Jens Axboe <axboe@kernel.dk>
Message-ID: <fe0066b7-5380-43ee-20b2-c9b17ba18e4f@kernel.dk>
Date:   Sun, 5 Jul 2020 15:00:47 -0600
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On 7/5/20 12:47 PM, Kanchan Joshi wrote:
> From: Selvakumar S <selvakuma.s1@samsung.com>
> 
> For zone-append, block-layer will return zone-relative offset via ret2
> of ki_complete interface. Make changes to collect it, and send to
> user-space using cqe->flags.
> 
> Signed-off-by: Selvakumar S <selvakuma.s1@samsung.com>
> Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
> Signed-off-by: Nitesh Shetty <nj.shetty@samsung.com>
> Signed-off-by: Javier Gonzalez <javier.gonz@samsung.com>
> ---
>  fs/io_uring.c | 21 +++++++++++++++++++--
>  1 file changed, 19 insertions(+), 2 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index 155f3d8..cbde4df 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -402,6 +402,8 @@ struct io_rw {
>  	struct kiocb			kiocb;
>  	u64				addr;
>  	u64				len;
> +	/* zone-relative offset for append, in sectors */
> +	u32			append_offset;
>  };

I don't like this very much at all. As it stands, the first cacheline
of io_kiocb is set aside for request-private data. io_rw is already
exactly 64 bytes, which means that you're now growing io_rw beyond
a cacheline and increasing the size of io_kiocb as a whole.

Maybe you can reuse io_rw->len for this, as that is only used on the
submission side of things.

-- 
Jens Axboe