[PATCH v5 1/9] task_isolation: vmstat: add quiet_vmstat_sync function

[Alex Belits <abelits@marvell.com>]

From: Chris Metcalf <cmetcalf@mellanox.com>

In commit f01f17d3705b ("mm, vmstat: make quiet_vmstat lighter")
the quiet_vmstat() function became asynchronous, in the sense that
the vmstat work was still scheduled to run on the core when the
function returned.  For task isolation, we need a synchronous
version of the function that guarantees that the vmstat worker
will not run on the core on return from the function.  Add a
quiet_vmstat_sync() function with that semantic.

Signed-off-by: Chris Metcalf <cmetcalf@mellanox.com>
Signed-off-by: Alex Belits <abelits@marvell.com>
---
 include/linux/vmstat.h | 2 ++
 mm/vmstat.c            | 9 +++++++++
 2 files changed, 11 insertions(+)

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 322dcbfcc933..300ce6648923 100644
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -284,6 +284,7 @@ extern void __dec_zone_state(struct zone *, enum zone_stat_item);
 extern void __dec_node_state(struct pglist_data *, enum node_stat_item);
 
 void quiet_vmstat(void);
+void quiet_vmstat_sync(void);
 void cpu_vm_stats_fold(int cpu);
 void refresh_zone_stat_thresholds(void);
 
@@ -391,6 +392,7 @@ static inline void __dec_node_page_state(struct page *page,
 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 void drain_zonestat(struct zone *zone,
 			struct per_cpu_pageset *pset) { }
diff --git a/mm/vmstat.c b/mm/vmstat.c
index 698bc0bc18d1..43999caf47a4 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -1936,6 +1936,15 @@ void quiet_vmstat(void)
 	refresh_cpu_vm_stats(false);
 }
 
+/*
+ * Synchronously quiet vmstat so the work is guaranteed not to run on return.
+ */
+void quiet_vmstat_sync(void)
+{
+	cancel_delayed_work_sync(this_cpu_ptr(&vmstat_work));
+	refresh_cpu_vm_stats(false);
+}
+
 /*
  * Shepherd worker thread that checks the
  * differentials of processors that have their worker
-- 
2.20.1