linux-kernel - Re: [PATCH 4/4] pipe_fs_i.h: add pipe_buf

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Date:   Sun, 13 Mar 2022 02:37:43 +0000
From:   Al Viro <viro@...iv.linux.org.uk>
To:     Max Kellermann <max.kellermann@...il.com>
Cc:     linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] pipe_fs_i.h: add pipe_buf_init()

On Fri, Feb 25, 2022 at 07:54:31PM +0100, Max Kellermann wrote:

>  			/* Insert it into the buffer array */
>  			buf = &pipe->bufs[head & mask];
> -			buf->page = page;
> -			buf->ops = &anon_pipe_buf_ops;
> -			buf->offset = 0;
> -			buf->len = 0;
> -			if (is_packetized(filp))
> -				buf->flags = PIPE_BUF_FLAG_PACKET;
> -			else
> -				buf->flags = PIPE_BUF_FLAG_CAN_MERGE;
> +			pipe_buf_init(buf, page, 0, 0,
> +				      &anon_pipe_buf_ops,
> +				      is_packetized(filp) ? PIPE_BUF_FLAG_PACKET : PIPE_BUF_FLAG_CAN_MERGE);

*cringe*
FWIW, packetized case is very rare, so how about turning that into
			pipe_buf_init(buf, page, 0, 0,
				      &anon_pipe_buf_ops,
				      PIPE_BUF_FLAG_CAN_MERGE);
			if (unlikely(is_packetized(filp)))
				buf->flags = PIPE_BUF_FLAG_PACKET;
Your pipe_buf_init() is inlined, so it shouldn't be worse from the optimizer
POV - it should be able to start with calculating that value and then storing
that, etc.