[PATCH 1/3] tty: port: replace get_zeroed_page() with kzalloc()

tty_port_alloc_xmit_buf() allocates the transmit buffer of a tty 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.

Replace use of get_zeroed_page() with kzalloc() and free_page() with
kfree().

Link: https://lore.kernel.org/all/[email protected]
Assisted-by: copilot:claude-opus
Signed-off-by: Mike Rapoport (Microsoft) <[email protected]>
---
 drivers/tty/tty_port.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/tty/tty_port.c b/drivers/tty/tty_port.c
index 54359310e293..44122921fc45 100644
--- a/drivers/tty/tty_port.c
+++ b/drivers/tty/tty_port.c
@@ -240,13 +240,13 @@ EXPORT_SYMBOL_GPL(tty_port_unregister_device);
 
 int tty_port_alloc_xmit_buf(struct tty_port *port)
 {
-	/* We may sleep in get_zeroed_page() */
+	/* We may sleep in kzalloc() */
 	guard(mutex)(&port->buf_mutex);
 
 	if (port->xmit_buf)
 		return 0;
 
-	port->xmit_buf = (u8 *)get_zeroed_page(GFP_KERNEL);
+	port->xmit_buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
 	if (port->xmit_buf == NULL)
 		return -ENOMEM;
 
@@ -259,7 +259,7 @@ EXPORT_SYMBOL(tty_port_alloc_xmit_buf);
 void tty_port_free_xmit_buf(struct tty_port *port)
 {
 	guard(mutex)(&port->buf_mutex);
-	free_page((unsigned long)port->xmit_buf);
+	kfree(port->xmit_buf);
 	port->xmit_buf = NULL;
 	INIT_KFIFO(port->xmit_fifo);
 }
@@ -288,7 +288,7 @@ static void tty_port_destructor(struct kref *kref)
 	/* check if last port ref was dropped before tty release */
 	if (WARN_ON(port->itty))
 		return;
-	free_page((unsigned long)port->xmit_buf);
+	kfree(port->xmit_buf);
 	tty_port_destroy(port);
 	if (port->ops && port->ops->destruct)
 		port->ops->destruct(port);

-- 
2.53.0