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Subject: Re: [PATCH v1] fs/io_uring: Hoist ret2 == -EAGAIN check in tail of
 io_write
To:     Noah Goldstein <goldstein.w.n@gmail.com>
Cc:     axboe@kernel.dk, asml.silence@gmail.com, io-uring@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <20211018070242.20325-1-goldstein.w.n@gmail.com>
From:   Hao Xu <haoxu@linux.alibaba.com>
Message-ID: <f27e1842-f22e-a40d-7055-6f924b13100f@linux.alibaba.com>
Date:   Mon, 18 Oct 2021 20:17:57 +0800
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在 2021/10/18 下午3:02, Noah Goldstein 写道:
> This commit reorganizes the branches in the tail of io_write so that
> the 'ret2 == -EAGAIN' check is not repeated and done first.
> 
> The previous version was duplicating the 'ret2 == -EAGAIN'. As well
> 'ret2 != -EAGAIN' gurantees the 'done:' path so it makes sense to
> move that check to the front before the likely more expensive branches
> which require memory derefences.
> 
> Signed-off-by: Noah Goldstein <goldstein.w.n@gmail.com>
> ---
> Generally I would want to rewrite this as:
> ```
> if (ret2 != -EAGAIN
>      || (req->flags & REQ_F_NOWAIT)
>      || (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL)))
>          kiocb_done(kiocb, ret2, issue_flags);
> else {
>      ...
> ```
To me, this one is clear enough and short, but I think better to:
if (ret2 != -EAGAIN || (req->flags & REQ_F_NOWAIT) ||
     (!force_nonblock && !(req->ctx->flags & IORING_SETUP_IOPOLL))

if the first line doesn't exceed the line limit.

Reviewed-by: Hao Xu <haoxu@linux.alibaba.com>
> 
> But the style of the file seems to be to use gotos. If the above is
> prefereable, let me know and I'll post a new version.
>   fs/io_uring.c | 9 ++++++---
>   1 file changed, 6 insertions(+), 3 deletions(-)
> 
> diff --git a/fs/io_uring.c b/fs/io_uring.c
> index d1e672e7a2d1..932fc84d70d3 100644
> --- a/fs/io_uring.c
> +++ b/fs/io_uring.c
> @@ -3648,12 +3648,15 @@ static int io_write(struct io_kiocb *req, unsigned int issue_flags)
>   	 */
>   	if (ret2 == -EOPNOTSUPP && (kiocb->ki_flags & IOCB_NOWAIT))
>   		ret2 = -EAGAIN;
> +
> +	if (ret2 != -EAGAIN)
> +		goto done;
>   	/* no retry on NONBLOCK nor RWF_NOWAIT */
> -	if (ret2 == -EAGAIN && (req->flags & REQ_F_NOWAIT))
> +	if (req->flags & REQ_F_NOWAIT)
>   		goto done;
> -	if (!force_nonblock || ret2 != -EAGAIN) {
> +	if (!force_nonblock) {
>   		/* IOPOLL retry should happen for io-wq threads */
> -		if (ret2 == -EAGAIN && (req->ctx->flags & IORING_SETUP_IOPOLL))
> +		if (req->ctx->flags & IORING_SETUP_IOPOLL)
>   			goto copy_iov;
>   done:
>   		kiocb_done(kiocb, ret2, issue_flags);
>