[PATCH v12 02/13] vmstat: add vmstat_idle function

[Chris Metcalf]

This function checks to see if a vmstat worker is not running,
and the vmstat diffs don't require an update.  The function is
called from the task-isolation code to see if we need to
actually do some work to quiet vmstat.

Acked-by: Christoph Lameter <cl@xxxxxxxxx>
Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxxxx>
---
 include/linux/vmstat.h |  2 ++
 mm/vmstat.c            | 12 ++++++++++++
 2 files changed, 14 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 43b2f1c33266..504ebd1fdf33 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -191,6 +191,7 @@ extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 
 void quiet_vmstat(void);
 void quiet_vmstat_sync(void);
+bool vmstat_idle(void);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -253,6 +254,7 @@ static inline void refresh_zone_stat_thresholds(void) { }
 static inline void cpu_vm_stats_fold(int cpu) { }
 static inline void quiet_vmstat(void) { }
 static inline void quiet_vmstat_sync(void) { }
+static inline bool vmstat_idle(void) { return true; }
 
 static inline void drain_zonestat(struct zone *zone,
 			struct per_cpu_pageset *pset) { }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 7a1cfe383349..fa34ea480ac0 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1469,6 +1469,18 @@ void quiet_vmstat_sync(void)
 }
 
 /*
+ * Report on whether vmstat processing is quiesced on the core currently:
+ * no vmstat worker running and no vmstat updates to perform.
+ */
+bool vmstat_idle(void)
+{
+	int cpu = smp_processor_id();
+	return cpumask_test_cpu(cpu, cpu_stat_off) &&
+		!delayed_work_pending(this_cpu_ptr(&vmstat_work)) &&
+		!need_update(cpu);
+}
+
+/*
  * Shepherd worker thread that checks the
  * differentials of processors that have their worker
  * threads for vm statistics updates disabled because of
-- 
2.7.2