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

[Mike Rapoport]

On Mon, Aug 31, 2026 at 05:02:54AM +0200, Jiri Slaby wrote:
> 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@xxxxxxxxxx
> > Assisted-by: copilot:claude-opus
> > Signed-off-by: Mike Rapoport (Microsoft) <rppt@xxxxxxxxxx>
> > ---
> >   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?

Sure, I also made this change in uart_free_xmit_buf().
 
> thanks,
> -- 
> js
> suse labs

-- 
Sincerely yours,
Mike.