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    Subject[PATCH 4.14 014/164] mm, slab: reschedule cache_reap() on the same CPU
    Date
    4.14-stable review patch.  If anyone has any objections, please let me know.

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

    From: Vlastimil Babka <vbabka@suse.cz>

    commit a9f2a846f0503e7d729f552e3ccfe2279010fe94 upstream.

    cache_reap() is initially scheduled in start_cpu_timer() via
    schedule_delayed_work_on(). But then the next iterations are scheduled
    via schedule_delayed_work(), i.e. using WORK_CPU_UNBOUND.

    Thus since commit ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND
    work on wq_unbound_cpumask CPUs") there is no guarantee the future
    iterations will run on the originally intended cpu, although it's still
    preferred. I was able to demonstrate this with
    /sys/module/workqueue/parameters/debug_force_rr_cpu. IIUC, it may also
    happen due to migrating timers in nohz context. As a result, some cpu's
    would be calling cache_reap() more frequently and others never.

    This patch uses schedule_delayed_work_on() with the current cpu when
    scheduling the next iteration.

    Link: http://lkml.kernel.org/r/20180411070007.32225-1-vbabka@suse.cz
    Fixes: ef557180447f ("workqueue: schedule WORK_CPU_UNBOUND work on wq_unbound_cpumask CPUs")
    Signed-off-by: Vlastimil Babka <vbabka@suse.cz>
    Acked-by: Pekka Enberg <penberg@kernel.org>
    Acked-by: Christoph Lameter <cl@linux.com>
    Cc: Joonsoo Kim <iamjoonsoo.kim@lge.com>
    Cc: David Rientjes <rientjes@google.com>
    Cc: Tejun Heo <tj@kernel.org>
    Cc: Lai Jiangshan <jiangshanlai@gmail.com>
    Cc: John Stultz <john.stultz@linaro.org>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: Stephen Boyd <sboyd@kernel.org>
    Cc: <stable@vger.kernel.org>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

    ---
    mm/slab.c | 3 ++-
    1 file changed, 2 insertions(+), 1 deletion(-)

    --- a/mm/slab.c
    +++ b/mm/slab.c
    @@ -4080,7 +4080,8 @@ next:
    next_reap_node();
    out:
    /* Set up the next iteration */
    - schedule_delayed_work(work, round_jiffies_relative(REAPTIMEOUT_AC));
    + schedule_delayed_work_on(smp_processor_id(), work,
    + round_jiffies_relative(REAPTIMEOUT_AC));
    }

    #ifdef CONFIG_SLABINFO

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