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    Subject[PATCH 3.4 123/172] writeback: add missing INITIAL_JIFFIES init in global_update_bandwidth()
    Date
    From: Tejun Heo <tj@kernel.org>

    3.4.108-rc1 review patch. If anyone has any objections, please let me know.

    ------------------


    commit 7d70e15480c0450d2bfafaad338a32e884fc215e upstream.

    global_update_bandwidth() uses static variable update_time as the
    timestamp for the last update but forgets to initialize it to
    INITIALIZE_JIFFIES.

    This means that global_dirty_limit will be 5 mins into the future on
    32bit and some large amount jiffies into the past on 64bit. This
    isn't critical as the only effect is that global_dirty_limit won't be
    updated for the first 5 mins after booting on 32bit machines,
    especially given the auxiliary nature of global_dirty_limit's role -
    protecting against global dirty threshold's sudden dips; however, it
    does lead to unintended suboptimal behavior. Fix it.

    Fixes: c42843f2f0bb ("writeback: introduce smoothed global dirty limit")
    Signed-off-by: Tejun Heo <tj@kernel.org>
    Acked-by: Jan Kara <jack@suse.cz>
    Cc: Wu Fengguang <fengguang.wu@intel.com>
    Cc: Jens Axboe <axboe@kernel.dk>
    Signed-off-by: Jens Axboe <axboe@fb.com>
    Signed-off-by: Zefan Li <lizefan@huawei.com>
    ---
    mm/page-writeback.c | 2 +-
    1 file changed, 1 insertion(+), 1 deletion(-)

    diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    index 057884c..b747dcd 100644
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -831,7 +831,7 @@ static void global_update_bandwidth(unsigned long thresh,
    unsigned long now)
    {
    static DEFINE_SPINLOCK(dirty_lock);
    - static unsigned long update_time;
    + static unsigned long update_time = INITIAL_JIFFIES;

    /*
    * check locklessly first to optimize away locking for the most time
    --
    1.9.1


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