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>

diff --git a/drivers/char/tty_buffer.c b/drivers/char/tty_buffer.c
index 66fa4e10d76bd47e1192a4593a488e8491e09b68..f27c4d6d956ec7e6501a6990ffd81b736750d478 100644 (file)
--- 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))

diff --git a/include/linux/tty.h b/include/linux/tty.h
index 6abfcf5b5887c030bfea8b4162a006d3f21a2502..d96e5882f12912038eabbd21e790c13fa689533c 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -68,6 +68,16 @@ struct tty_buffer {
        unsigned long data[0];
 };
 
+/*
+ * We default to dicing tty buffer allocations to this many characters
+ * in order to avoid multiple page allocations. We assume tty_buffer itself
+ * is under 256 bytes. See tty_buffer_find for the allocation logic this
+ * must match
+ */
+
+#define TTY_BUFFER_PAGE                ((PAGE_SIZE  - 256) / 2)
+
+
 struct tty_bufhead {
        struct delayed_work work;
        spinlock_t lock;