[PATCH v8 02/14] 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.

Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
---
 include/linux/vmstat.h |  2 ++
 mm/vmstat.c            | 10 ++++++++++
 2 files changed, 12 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index c013b8d8e434..34e3b768e432 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -212,6 +212,7 @@ extern void dec_zone_state(struct zone *, enum zone_stat_item);
 extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 
 void quiet_vmstat(void);
+bool vmstat_idle(void);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -274,6 +275,7 @@ static inline void refresh_cpu_vm_stats(int cpu) { }
 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 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 a9c446353c7e..05fa1f0eefc8 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1431,6 +1431,16 @@ static bool need_update(int cpu)
 	return false;
 }
 
+/*
+ * 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) && !need_update(cpu);
+}
+
 
 /*
  * Shepherd worker thread that checks the
-- 
2.1.2

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