[PATCH v7 2/2] mm: make lru_add_drain_all() selective

[Chris Metcalf]

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.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
v7: try a version with callbacks instead of cpu masks.
Either this or v6 seem like reasonable solutions.

v6: add Tejun's Acked-by, and add missing get/put_cpu_online to
lru_add_drain_all().

v5: provide validity checking on the cpumask for schedule_on_cpu_mask.
By providing an all-or-nothing EINVAL check, we impose the requirement
that the calling code actually know clearly what it's trying to do.
(Note: no change to the mm/swap.c commit)

v4: don't lose possible -ENOMEM in schedule_on_each_cpu()
(Note: no change to the mm/swap.c commit)

v3: split commit into two, one for workqueue and one for mm, though both
should probably be taken through -mm.

 mm/swap.c | 21 ++++++++++++++++++++-
 1 file changed, 20 insertions(+), 1 deletion(-)

diff --git a/mm/swap.c b/mm/swap.c
index 4a1d0d2..fe3a488 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;
+}
+
 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);
@@ -673,6 +683,14 @@ void lru_add_drain(void)
 	put_cpu();
 }
 
+static bool lru_add_drain_cond(void *data, int cpu)
+{
+	return 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);
+}
+
 static void lru_add_drain_per_cpu(struct work_struct *dummy)
 {
 	lru_add_drain();
@@ -683,7 +701,8 @@ static void lru_add_drain_per_cpu(struct work_struct *dummy)
  */
 int lru_add_drain_all(void)
 {
-	return schedule_on_each_cpu(lru_add_drain_per_cpu);
+	return schedule_on_each_cpu_cond(lru_add_drain_per_cpu,
+					 lru_add_drain_cond, NULL);
 }
 
 /*
-- 
1.8.3.1

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