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

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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>
This commit is contained in:
Mel Gorman 2010-03-02 22:24:19 +00:00 committed by Greg Kroah-Hartman
parent 87a6aca504
commit 352fa6ad16
1 changed files with 5 additions and 4 deletions
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9
include/linux/tty.h
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@ -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 {