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    Subject[PATCH] kswapd: assign new_order and new_classzone_idx after wakeup in sleeping
    There 2 place to read pgdat in kswapd. One is return from a successful
    balance, another is waked up from sleeping. But the new_order and
    new_classzone_idx are not assigned after kswapd_try_to_sleep(), that
    will cause a bug in the following scenario.

    After the last time successful balance, kswapd goes to sleep. So the
    new_order and new_classzone_idx were assigned to 0 and MAX-1 since there
    is no new wakeup during last time balancing. Now, a new wakeup came and
    finish balancing successful with order > 0. But since new_order is still
    0, this time successful balancing were judged as a failed balance. so,
    if there is another new wakeup coming during balancing, kswapd cann't
    read this and still want to try to sleep. And if the new wakeup is a
    tighter request, kswapd may goes to sleep, not to do balancing. That is

    So, to avoid above problem, the new_order and new_classzone_idx need to
    be assigned for later successful comparison.

    Paidrag Brady, Could like do a retry for your problem on this patch?

    Signed-off-by: Alex Shi <>
    Acked-by: Mel Gorman <>
    mm/vmscan.c | 2 ++
    1 files changed, 2 insertions(+), 0 deletions(-)

    diff --git a/mm/vmscan.c b/mm/vmscan.c
    index 7ef6912..eb7bcce 100644
    --- a/mm/vmscan.c
    +++ b/mm/vmscan.c
    @@ -2850,6 +2850,8 @@ static int kswapd(void *p)
    kswapd_try_to_sleep(pgdat, order, classzone_idx);
    order = pgdat->kswapd_max_order;
    classzone_idx = pgdat->classzone_idx;
    + new_order = order;
    + new_classzone_idx = classzone_idx;
    pgdat->kswapd_max_order = 0;
    pgdat->classzone_idx = pgdat->nr_zones - 1;

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      Last update: 2011-07-29 03:35    [W:0.028 / U:7.712 seconds]
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