Introduce a CPU-specific variable namely vmstat_dirty to indicate
if a vmstat imbalance is present for a given CPU. Therefore, at
the appropriate time, we can fold all the remaining differentials.
This patch also provides trivial helpers for modification and testing.

Signed-off-by: Aaron Tomlin <atomlin@redhat.com>
---
 mm/vmstat.c | 16 ++++++++++++++++
 1 file changed, 16 insertions(+)

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 90af9a8572f5..24c67b2e58fd 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -195,6 +195,22 @@ void fold_vm_numa_events(void)
 #endif
 
 #ifdef CONFIG_SMP
+static DEFINE_PER_CPU_ALIGNED(bool, vmstat_dirty);
+
+static inline void vmstat_mark_dirty(void)
+{
+	this_cpu_write(vmstat_dirty, true);
+}
+
+static inline void vmstat_clear_dirty(void)
+{
+	this_cpu_write(vmstat_dirty, false);
+}
+
+static inline bool is_vmstat_dirty(void)
+{
+	return this_cpu_read(vmstat_dirty);
+}
 
 int calculate_pressure_threshold(struct zone *zone)
 {
-- 
2.37.1