Commit 352fa6ad authored Mar 02, 2010 by Mel Gorman Committed by Greg Kroah-Hartman Mar 19, 2010

tty: Take a 256 byte padding into account when buffering below sub-page units



The TTY layer takes some care to ensure that only sub-page allocations
are made with interrupts disabled. It does this by setting a goal of
"TTY_BUFFER_PAGE" to allocate. Unfortunately, while TTY_BUFFER_PAGE takes the
size of tty_buffer into account, it fails to account that tty_buffer_find()
rounds the buffer size out to the next 256 byte boundary before adding on
the size of the tty_buffer.

This patch adjusts the TTY_BUFFER_PAGE calculation to take into account the
size of the tty_buffer and the padding. Once applied, tty_buffer_alloc()
should not require high-order allocations.

Signed-off-by: Mel Gorman <mel@csn.ul.ie>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

parent 87a6aca5

include/linux/tty.h

+5 −4

Original line number	Diff line number	Diff line
		@@ -70,12 +70,13 @@ struct tty_buffer {

		/*
		* 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
		* in order to avoid multiple page allocations. We know the size of
		* tty_buffer itself but it must also be taken into account that the
		* the buffer is 256 byte aligned. See tty_buffer_find for the allocation
		* logic this must match
		*/

		#define TTY_BUFFER_PAGE ((PAGE_SIZE - 256) / 2)
		#define TTY_BUFFER_PAGE (((PAGE_SIZE - sizeof(struct tty_buffer)) / 2) & ~0xFF)


		struct tty_bufhead {