On Thu 31-07-14 11:30:19, Lai Jiangshan wrote:
> 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.
Why? Just because there is general recommendation for using
cpumask_var_t rather than cpumask?
In this particular case cpumask shouldn't matter much as it is static.
Your code will work as well, but I do not see any strong reason to
change it just to get rid of cpumask which is not on stack.
> CC: akpm@xxxxxxxxxxxxxxxxxxxx
> CC: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> CC: Mel Gorman <mgorman@xxxxxxx>
> CC: Tejun Heo <tj@xxxxxxxxxx>
> CC: Christoph Lameter <cl@xxxxxxxxxx>
> CC: Frederic Weisbecker <fweisbec@xxxxxxxxx>
> Signed-off-by: Lai Jiangshan <laijs@xxxxxxxxxxxxxx>
> ---
> 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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--
Michal Hocko
SUSE Labs
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