It is suggested that cpumask_var_t and alloc_cpumask_var() should be used
instead of struct cpumask.  But I don't want to add this complicity nor
leave this unwelcome "static struct cpumask has_work;", so I just remove
it and use flush_work() to perform on all online drain_work.  flush_work()
performs very quickly on initialized but unused work item, thus we don't
need the struct cpumask has_work for performance.

CC: a...@linux-foundation.org
CC: Chris Metcalf <cmetc...@tilera.com>
CC: Mel Gorman <mgor...@suse.de>
CC: Tejun Heo <t...@kernel.org>
CC: Christoph Lameter <c...@gentwo.org>
CC: Frederic Weisbecker <fweis...@gmail.com>
Signed-off-by: Lai Jiangshan <la...@cn.fujitsu.com>
---
 mm/swap.c |   11 ++++-------
 1 files changed, 4 insertions(+), 7 deletions(-)

diff --git a/mm/swap.c b/mm/swap.c
index 9e8e347..bb524ca 100644
--- a/mm/swap.c
+++ b/mm/swap.c
@@ -833,27 +833,24 @@ static DEFINE_PER_CPU(struct work_struct, 
lru_add_drain_work);
 void lru_add_drain_all(void)
 {
        static DEFINE_MUTEX(lock);
-       static struct cpumask has_work;
        int cpu;
 
        mutex_lock(&lock);
        get_online_cpus();
-       cpumask_clear(&has_work);
 
        for_each_online_cpu(cpu) {
                struct work_struct *work = &per_cpu(lru_add_drain_work, cpu);
 
+               INIT_WORK(work, lru_add_drain_per_cpu);
+
                if (pagevec_count(&per_cpu(lru_add_pvec, cpu)) ||
                    pagevec_count(&per_cpu(lru_rotate_pvecs, cpu)) ||
                    pagevec_count(&per_cpu(lru_deactivate_pvecs, cpu)) ||
-                   need_activate_page_drain(cpu)) {
-                       INIT_WORK(work, lru_add_drain_per_cpu);
+                   need_activate_page_drain(cpu))
                        schedule_work_on(cpu, work);
-                       cpumask_set_cpu(cpu, &has_work);
-               }
        }
 
-       for_each_cpu(cpu, &has_work)
+       for_each_online_cpu(cpu)
                flush_work(&per_cpu(lru_add_drain_work, cpu));
 
        put_online_cpus();
-- 
1.7.4.4

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