On Wed, 14 Aug 2013 16:22:18 -0400 Chris Metcalf <cmetcalf@xxxxxxxxxx> wrote:
> This change makes lru_add_drain_all() only selectively interrupt
> the cpus that have per-cpu free pages that can be drained.
>
> This is important in nohz mode where calling mlockall(), for
> example, otherwise will interrupt every core unnecessarily.
>
I think the patch will work, but it's a bit sad to no longer gain the
general ability to do schedule_on_some_cpus(). Oh well.
> --- a/include/linux/swap.h
> +++ b/include/linux/swap.h
> @@ -247,7 +247,7 @@ extern void activate_page(struct page *);
> extern void mark_page_accessed(struct page *);
> extern void lru_add_drain(void);
> extern void lru_add_drain_cpu(int cpu);
> -extern int lru_add_drain_all(void);
> +extern void lru_add_drain_all(void);
> extern void rotate_reclaimable_page(struct page *page);
> extern void deactivate_page(struct page *page);
> extern void swap_setup(void);
> diff --git a/mm/swap.c b/mm/swap.c
> index 4a1d0d2..8d19543 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -405,6 +405,11 @@ static void activate_page_drain(int cpu)
> pagevec_lru_move_fn(pvec, __activate_page, NULL);
> }
>
> +static bool need_activate_page_drain(int cpu)
> +{
> + return pagevec_count(&per_cpu(activate_page_pvecs, cpu)) != 0;
> +}
static int need_activate_page_drain(int cpu)
{
return pagevec_count(&per_cpu(activate_page_pvecs, cpu));
}
would be shorter and faster. bool rather sucks that way. It's a
performance-vs-niceness thing. I guess one has to look at the call
frequency when deciding.
> void activate_page(struct page *page)
> {
> if (PageLRU(page) && !PageActive(page) && !PageUnevictable(page)) {
> @@ -422,6 +427,11 @@ static inline void activate_page_drain(int cpu)
> {
> }
>
> +static bool need_activate_page_drain(int cpu)
> +{
> + return false;
> +}
> +
> void activate_page(struct page *page)
> {
> struct zone *zone = page_zone(page);
> @@ -678,12 +688,36 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
> lru_add_drain();
> }
>
> -/*
> - * Returns 0 for success
> - */
> -int lru_add_drain_all(void)
> +static DEFINE_PER_CPU(struct work_struct, lru_add_drain_work);
> +
> +void lru_add_drain_all(void)
> {
> - return schedule_on_each_cpu(lru_add_drain_per_cpu);
> + static DEFINE_MUTEX(lock);
> + static struct cpumask has_work;
> + int cpu;
> +
> + mutex_lock(&lock);
This is a bit scary but I expect it will be OK - later threads will
just twiddle thumbs while some other thread does all or most of their
work for them.
> + get_online_cpus();
> + cpumask_clear(&has_work);
> +
> + for_each_online_cpu(cpu) {
> + struct work_struct *work = &per_cpu(lru_add_drain_work, 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);
This initialization is only needed once per boot but I don't see a
convenient way of doing this.
> + schedule_work_on(cpu, work);
> + cpumask_set_cpu(cpu, &has_work);
> + }
> + }
> +
> + for_each_cpu(cpu, &has_work)
for_each_online_cpu()?
> + flush_work(&per_cpu(lru_add_drain_work, cpu));
> +
> + put_online_cpus();
> + mutex_unlock(&lock);
> }
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