linux-kernel - Re: [PATCH tty-next 5/5] tty: Halve flip buffer GFP

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Message-ID: <20131209010112.GA31052@kroah.com>
Date:	Sun, 8 Dec 2013 17:01:12 -0800
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Jiri Slaby <jslaby@...e.cz>, linux-kernel@...r.kernel.org,
	linux-serial@...r.kernel.org
Subject: Re: [PATCH tty-next 5/5] tty: Halve flip buffer GFP_ATOMIC memory
 consumption

On Fri, Nov 22, 2013 at 12:09:58PM -0500, Peter Hurley wrote:
> tty flip buffers use GFP_ATOMIC allocations for received data
> which is to be processed by the line discipline. For each byte
> received, an extra byte is used to indicate the error status of
> that byte.
> 
> Instead, if the received data is error-free, encode the entire
> buffer without status bytes.
> 
> Signed-off-by: Peter Hurley <peter@...leysoftware.com>
> ---
>  drivers/tty/tty_buffer.c | 45 +++++++++++++++++++++++++++++++++++----------
>  include/linux/tty.h      |  4 ++++
>  include/linux/tty_flip.h |  8 ++++++--
>  3 files changed, 45 insertions(+), 12 deletions(-)
> 
> diff --git a/drivers/tty/tty_buffer.c b/drivers/tty/tty_buffer.c
> index 6a3620e..c4fe20e 100644
> --- a/drivers/tty/tty_buffer.c
> +++ b/drivers/tty/tty_buffer.c
> @@ -100,6 +100,7 @@ static void tty_buffer_reset(struct tty_buffer *p, size_t size)
>  	p->next = NULL;
>  	p->commit = 0;
>  	p->read = 0;
> +	p->flags = 0;
>  }
>  
>  /**
> @@ -230,31 +231,49 @@ void tty_buffer_flush(struct tty_struct *tty)
>   *	tty_buffer_request_room		-	grow tty buffer if needed
>   *	@tty: tty structure
>   *	@size: size desired
> + *	@flags: buffer flags if new buffer allocated (default = 0)
>   *
>   *	Make at least size bytes of linear space available for the tty
>   *	buffer. If we fail return the size we managed to find.
> + *
> + *	Will change over to a new buffer if the current buffer is encoded as
> + *	TTY_NORMAL (so has no flags buffer) and the new buffer requires
> + *	a flags buffer.
>   */
> -int tty_buffer_request_room(struct tty_port *port, size_t size)
> +int __tty_buffer_request_room(struct tty_port *port, size_t size, int flags)
>  {
>  	struct tty_bufhead *buf = &port->buf;
>  	struct tty_buffer *b, *n;
> -	int left;
> +	int left, change;
>  
>  	b = buf->tail;
> -	left = b->size - b->used;
> +	if (b->flags & TTYB_NORMAL)
> +		left = 2 * b->size - b->used;
> +	else
> +		left = b->size - b->used;
>  
> -	if (left < size) {
> +	change = (b->flags & TTYB_NORMAL) && (~flags & TTYB_NORMAL);
> +	if (change || left < size) {
>  		/* This is the slow path - looking for new buffers to use */
>  		if ((n = tty_buffer_alloc(port, size)) != NULL) {
> +			n->flags = flags;
>  			buf->tail = n;
>  			b->commit = b->used;
>  			smp_mb();
>  			b->next = n;
> -		} else
> +		} else if (change)
> +			size = 0;
> +		else
>  			size = left;
>  	}
>  	return size;
>  }
> +EXPORT_SYMBOL_GPL(__tty_buffer_request_room);

Why are you exporting this?  There is no function prototype anywhere, so
no one can even try to call it, it should just be static, right?

I've applied the first 4 patches in this series, care to fix this one
up?

thanks,

greg k-h
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