Re: [PATCH 2/3] serial: core: replace get_zeroed_page() with kzalloc()

[Jiri Slaby <jirislaby@kernel.org>]

On 30. 08. 26, 9:49, Mike Rapoport (Microsoft) wrote:
> uart_alloc_xmit_buf() allocates the transmit buffer of a serial port. The
> buffer only backs the port's kfifo, the data being sent is copied in and
> out of it.
> 
> This buffer can be allocated with kmalloc() as there's nothing special
> about it to go directly to the page allocator.
> 
> kmalloc() provides a better API that does not require ugly casts and
> kfree() does not need to know the size of the freed object.
> 
> Performance difference between kmalloc() and __get_free_pages() is not
> measurable as both allocators take an object/page from a per-CPU list for
> fast path allocations.
> 
> For the slow path the performance is anyway determined by the amount of
> reclaim involved rather than by what allocator is used.
> 
> While on it, make the local variable holding the buffer a pointer to get
> rid of the casts.
> 
> Replace use of get_zeroed_page() with kzalloc() and free_page() with
> kfree().
> 
> Link: https://lore.kernel.org/all/635405e4-9423-4a25-a6e7-e03c8ea0bcbe@redhat.com
> Assisted-by: copilot:claude-opus
> Signed-off-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
> ---
>   drivers/tty/serial/serial_core.c | 16 ++++++++--------
>   1 file changed, 8 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
> index 95774b0f1484..f12ce7d190fe 100644
> --- a/drivers/tty/serial/serial_core.c
> +++ b/drivers/tty/serial/serial_core.c
> @@ -247,29 +247,29 @@ static int uart_alloc_xmit_buf(struct tty_port *port)
>   	struct uart_state *state = container_of(port, struct uart_state, port);
>   	struct uart_port *uport;
>   	unsigned long flags;
> -	unsigned long page;

1:

> +	unsigned char *buf;
>   
>   	/*
>   	 * Initialise and allocate the transmit and temporary
>   	 * buffer.
>   	 */
> -	page = get_zeroed_page(GFP_KERNEL);
> -	if (!page)
> +	buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
> +	if (!buf)
>   		return -ENOMEM;
>   
>   	uport = uart_port_ref_lock(state, &flags);
>   	if (!state->port.xmit_buf) {
> -		state->port.xmit_buf = (unsigned char *)page;
> +		state->port.xmit_buf = buf;

xmit_buf is u8 *. This uchar was omitted when I was changing the type 
back then. Could you use the right type at 1b now?

thanks,
-- 
js
suse labs