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    Subject[tip:smp/hotplug] mm/writeback: Convert to hotplug state machine
    Commit-ID:  9505a0689c12e1a1304d822befbec67797de5544
    Gitweb: http://git.kernel.org/tip/9505a0689c12e1a1304d822befbec67797de5544
    Author: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    AuthorDate: Thu, 18 Aug 2016 14:57:20 +0200
    Committer: Thomas Gleixner <tglx@linutronix.de>
    CommitDate: Tue, 6 Sep 2016 16:20:29 +0200

    mm/writeback: Convert to hotplug state machine

    Install the callbacks via the state machine and let the core invoke
    the callbacks on the already online CPUs.

    Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
    Cc: Peter Zijlstra <peterz@infradead.org>
    Cc: Jens Axboe <axboe@fb.com>
    Cc: linux-mm@kvack.org
    Cc: rt@linutronix.de
    Cc: Tejun Heo <tj@kernel.org>
    Link: http://lkml.kernel.org/r/20160818125731.27256-6-bigeasy@linutronix.de
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

    ---
    include/linux/cpuhotplug.h | 1 +
    mm/page-writeback.c | 26 +++++++-------------------
    2 files changed, 8 insertions(+), 19 deletions(-)

    diff --git a/include/linux/cpuhotplug.h b/include/linux/cpuhotplug.h
    index b6c2ef7..e417a05 100644
    --- a/include/linux/cpuhotplug.h
    +++ b/include/linux/cpuhotplug.h
    @@ -16,6 +16,7 @@ enum cpuhp_state {
    CPUHP_X86_APB_DEAD,
    CPUHP_VIRT_NET_DEAD,
    CPUHP_SLUB_DEAD,
    + CPUHP_MM_WRITEBACK_DEAD,
    CPUHP_WORKQUEUE_PREP,
    CPUHP_POWER_NUMA_PREPARE,
    CPUHP_HRTIMERS_PREPARE,
    diff --git a/mm/page-writeback.c b/mm/page-writeback.c
    index f4cd7d8..28d6f36 100644
    --- a/mm/page-writeback.c
    +++ b/mm/page-writeback.c
    @@ -2080,26 +2080,12 @@ void writeback_set_ratelimit(void)
    ratelimit_pages = 16;
    }

    -static int
    -ratelimit_handler(struct notifier_block *self, unsigned long action,
    - void *hcpu)
    +static int page_writeback_cpu_online(unsigned int cpu)
    {
    -
    - switch (action & ~CPU_TASKS_FROZEN) {
    - case CPU_ONLINE:
    - case CPU_DEAD:
    - writeback_set_ratelimit();
    - return NOTIFY_OK;
    - default:
    - return NOTIFY_DONE;
    - }
    + writeback_set_ratelimit();
    + return 0;
    }

    -static struct notifier_block ratelimit_nb = {
    - .notifier_call = ratelimit_handler,
    - .next = NULL,
    -};
    -
    /*
    * Called early on to tune the page writeback dirty limits.
    *
    @@ -2122,8 +2108,10 @@ void __init page_writeback_init(void)
    {
    BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));

    - writeback_set_ratelimit();
    - register_cpu_notifier(&ratelimit_nb);
    + cpuhp_setup_state(CPUHP_AP_ONLINE_DYN, "mm/writeback:online",
    + page_writeback_cpu_online, NULL);
    + cpuhp_setup_state(CPUHP_MM_WRITEBACK_DEAD, "mm/writeback:dead", NULL,
    + page_writeback_cpu_online);
    }

    /**
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