tty: Keep the default buffering to sub-page units

We allocate during interrupts so while our buffering is normally diced up
small anyway on some hardware at speed we can pressure the VM excessively
for page pairs. We don't really need big buffers to be linear so don't try
so hard.

In order to make this work well we will tidy up excess callers to request_room,
which cannot itself enforce this break up.

Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 4 insertions, 2 deletions

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 66fa4e10d76b..f27c4d6d956e 100644
--- a/drivers/char/tty_buffer.c
+++ b/drivers/char/tty_buffer.c
@@ -247,7 +247,8 @@ int tty_insert_flip_string(struct tty_struct *tty, const unsigned char *chars,
 {
         int copied = 0;
         do {
-                int space = tty_buffer_request_room(tty, size - copied);
+                int goal = min(size - copied, TTY_BUFFER_PAGE);
+                int space = tty_buffer_request_room(tty, goal);
                 struct tty_buffer *tb = tty->buf.tail;
                 /* If there is no space then tb may be NULL */
                 if (unlikely(space == 0))
@@ -283,7 +284,8 @@ int tty_insert_flip_string_flags(struct tty_struct *tty,
 {
         int copied = 0;
         do {
-                int space = tty_buffer_request_room(tty, size - copied);
+                int goal = min(size - copied, TTY_BUFFER_PAGE);
+                int space = tty_buffer_request_room(tty, goal);
                 struct tty_buffer *tb = tty->buf.tail;
                 /* If there is no space then tb may be NULL */
                 if (unlikely(space == 0))