[PATCH] memcg: event control at vmpressure.

[Hyunhee Kim <hyunhee.kim@xxxxxxxxxxx>]

In vmpressure, events are sent to the user space continuously
until the memory state changes. This becomes overheads for user space module
and also consumes power consumption. So, with this patch, vmpressure
remembers
the current level and only sends the event only when new memory state is
different from the current level.

Signed-off-by: Hyunhee Kim <hyunhee.kim@xxxxxxxxxxx>
Signed-off-by: Kyungmin Park <kyungmin.park@xxxxxxxxxxx>
---
 include/linux/vmpressure.h |    2 ++
 mm/vmpressure.c            |    4 +++-
 2 files changed, 5 insertions(+), 1 deletion(-)

diff --git a/include/linux/vmpressure.h b/include/linux/vmpressure.h
index 76be077..fa0c0d2 100644
--- a/include/linux/vmpressure.h
+++ b/include/linux/vmpressure.h
@@ -20,6 +20,8 @@ struct vmpressure {
 	struct mutex events_lock;
 
 	struct work_struct work;
+
+	int current_level;
 };
 
 struct mem_cgroup;
diff --git a/mm/vmpressure.c b/mm/vmpressure.c
index 736a601..5f6609c 100644
--- a/mm/vmpressure.c
+++ b/mm/vmpressure.c
@@ -152,9 +152,10 @@ static bool vmpressure_event(struct vmpressure *vmpr,
 	mutex_lock(&vmpr->events_lock);
 
 	list_for_each_entry(ev, &vmpr->events, node) {
-		if (level >= ev->level) {
+		if (level >= ev->level && level != vmpr->current_level) {
 			eventfd_signal(ev->efd, 1);
 			signalled = true;
+			vmpr->current_level = level;
 		}
 	}
 
@@ -371,4 +372,5 @@ void vmpressure_init(struct vmpressure *vmpr)
 	mutex_init(&vmpr->events_lock);
 	INIT_LIST_HEAD(&vmpr->events);
 	INIT_WORK(&vmpr->work, vmpressure_work_fn);
+	vmpr->current_level = -1;
 }
-- 
1.7.9.5


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