[PATCH v4 1/2] mm, vmstat: calculate particular vm event

[Ebru Akagunduz]

Currently, vmstat can calculate specific vm event with all_vm_events()
however it allocates all vm events to stack. This patch introduces
a helper to sum value of a specific vm event over all cpu, without
loading all the events.

Signed-off-by: Ebru Akagunduz <ebru.akagunduz@xxxxxxxxx>
Suggested-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Acked-by: Kirill A. Shutemov <kirill.shutemov@xxxxxxxxxxxxxxx>
Reviewed-by: Rik van Riel <riel@xxxxxxxxxx>
Acked-by: Vlastimil Babka <vbabka@xxxxxxx>
---
Changes in v2:
 - this patch newly created in this version
 - create sum event function to
   calculate particular vm event (Kirill A. Shutemov)

Changes in v3:
 - add dummy definition of sum_vm_event
   when CONFIG_VM_EVENTS is not set
   (Kirill A. Shutemov)

Changes in v4:
 - add Suggested-by tag (Vlastimil Babka)

 include/linux/vmstat.h |  6 ++++++
 mm/vmstat.c            | 12 ++++++++++++
 2 files changed, 18 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 73fae8c..e5ec287 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -53,6 +53,8 @@ static inline void count_vm_events(enum vm_event_item item, long delta)
 
 extern void all_vm_events(unsigned long *);
 
+extern unsigned long sum_vm_event(enum vm_event_item item);
+
 extern void vm_events_fold_cpu(int cpu);
 
 #else
@@ -73,6 +75,10 @@ static inline void __count_vm_events(enum vm_event_item item, long delta)
 static inline void all_vm_events(unsigned long *ret)
 {
 }
+static inline unsigned long sum_vm_event(enum vm_event_item item)
+{
+	return 0;
+}
 static inline void vm_events_fold_cpu(int cpu)
 {
 }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 5e43004..b76d664 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -34,6 +34,18 @@
 DEFINE_PER_CPU(struct vm_event_state, vm_event_states) = {{0}};
 EXPORT_PER_CPU_SYMBOL(vm_event_states);
 
+unsigned long sum_vm_event(enum vm_event_item item)
+{
+	int cpu;
+	unsigned long ret = 0;
+
+	get_online_cpus();
+	for_each_online_cpu(cpu)
+		ret += per_cpu(vm_event_states, cpu).event[item];
+	put_online_cpus();
+	return ret;
+}
+
 static void sum_vm_events(unsigned long *ret)
 {
 	int cpu;
-- 
1.9.1