[PATCH v6 1/6] vmstat: provide a function to quiet down the diff processing

[Chris Metcalf <cmetcalf@ezchip.com>]

From: Christoph Lameter <cl@linux.com>

quiet_vmstat() can be called in anticipation of a OS "quiet" period
where no tick processing should be triggered. quiet_vmstat() will fold
all pending differentials into the global counters and disable the
vmstat_worker processing.

Note that the shepherd thread will continue scanning the differentials
from another processor and will reenable the vmstat workers if it
detects any changes.

Signed-off-by: Christoph Lameter <cl@linux.com>
---
 include/linux/vmstat.h |  2 ++
 mm/vmstat.c            | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 82e7db7f7100..c013b8d8e434 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -211,6 +211,7 @@ extern void __inc_zone_state(struct zone *, enum zone_stat_item);
 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);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -272,6 +273,7 @@ static inline void __dec_zone_page_state(struct page *page,
 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 void drain_zonestat(struct zone *zone,
 			struct per_cpu_pageset *pset) { }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 4f5cd974e11a..cf7d324f16e2 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1394,6 +1394,20 @@ static void vmstat_update(struct work_struct *w)
 }
 
 /*
+ * Switch off vmstat processing and then fold all the remaining differentials
+ * until the diffs stay at zero. The function is used by NOHZ and can only be
+ * invoked when tick processing is not active.
+ */
+void quiet_vmstat(void)
+{
+	do {
+		if (!cpumask_test_and_set_cpu(smp_processor_id(), cpu_stat_off))
+			cancel_delayed_work(this_cpu_ptr(&vmstat_work));
+
+	} while (refresh_cpu_vm_stats());
+}
+
+/*
  * Check if the diffs for a certain cpu indicate that
  * an update is needed.
  */
-- 
2.1.2