Commit d9661adf authored by Alan Cox's avatar Alan Cox Committed by Greg Kroah-Hartman
Browse files

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: default avatarAlan Cox <alan@linux.intel.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent 4165fe4e

drivers/char/tty_buffer.c

+4 −2
Original line number Diff line number Diff line
@@ -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))

include/linux/tty.h

+10 −0
Original line number Diff line number Diff line
@@ -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;

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