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    Subject[PATCH 2/7] tty: Take a 256 byte padding into account when buffering below sub-page units
    Date
    From: Mel Gorman <mel@csn.ul.ie>

    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>
    ---
    include/linux/tty.h | 9 +++++----
    1 files changed, 5 insertions(+), 4 deletions(-)
    diff --git a/include/linux/tty.h b/include/linux/tty.h
    index 568369a..593228a 100644
    --- a/include/linux/tty.h
    +++ b/include/linux/tty.h
    @@ -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 {
    --
    1.7.0.2


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