linux-kernel - Re: [PATCH v2] fs/splice: don't block splice_direct_to

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Date:   Tue, 26 Sep 2023 12:21:53 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     Max Kellermann <max.kellermann@...os.com>
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, linux-fsdevel@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] fs/splice: don't block splice_direct_to_actor() after
 data was read

> +		/*
> +		 * After at least one byte was read from the input
> +		 * file, don't wait for blocking I/O in the following
> +		 * loop iterations; instead of blocking for arbitrary
> +		 * amounts of time in the kernel, let userspace decide
> +		 * how to proceed.  This avoids excessive latency if
> +		 * the output is being consumed faster than the input
> +		 * file can fill it (e.g. sendfile() from a slow hard
> +		 * disk to a fast network).
> +		 */
> +		flags |= SPLICE_F_NOWAIT;
> +

Hm, so the thing that is worrysome about this change is that this may
cause regressions afaict as this is a pretty significant change from
current behavior.