vmstat: make vmstat_updater deferrable again and shut down on idle

Currently the vmstat updater is not deferrable as a result of commit
ba4877b9ca51 ("vmstat: do not use deferrable delayed work for
vmstat_update").  This in turn can cause multiple interruptions of the
applications because the vmstat updater may run at

Make vmstate_update deferrable again and provide a function that folds
the differentials when the processor is going to idle mode thus
addressing the issue of the above commit in a clean way.

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

Fixes: ba4877b9ca51 ("vmstat: do not use deferrable delayed work for vmstat_update")
Signed-off-by: Christoph Lameter <cl@linux.com>
Cc: Michal Hocko <mhocko@suse.cz>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/include/linux/vmstat.h b/include/linux/vmstat.h
index 3e5d9075960f6c756ead3c60013f84f873206932..73fae8c4a5fb50d94b72f12bed28f98d170f5787 100644 (file)
--- a/include/linux/vmstat.h
+++ b/include/linux/vmstat.h
@@ -189,6 +189,7 @@ 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);
 
@@ -249,6 +250,7 @@ static inline void __dec_zone_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 drain_zonestat(struct zone *zone,
                        struct per_cpu_pageset *pset) { }

diff --git a/kernel/sched/idle.c b/kernel/sched/idle.c
index 4a2ef5a02fd3f91d7c4228378c23d5606bb73812..2489140a7c515d474db8213c6c91e581992ffcc2 100644 (file)
--- a/kernel/sched/idle.c
+++ b/kernel/sched/idle.c
@@ -219,6 +219,7 @@ static void cpu_idle_loop(void)
                 */
 
                __current_set_polling();
+               quiet_vmstat();
                tick_nohz_idle_enter();
 
                while (!need_resched()) {

diff --git a/mm/vmstat.c b/mm/vmstat.c
index c54fd2924f25af960462e474fa3583c633f9fcc8..83a003bc3cae54e3c2b1071249a5c282f70d3220 100644 (file)
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -460,7 +460,7 @@ static int fold_diff(int *diff)
  *
  * The function returns the number of global counters updated.
  */
-static int refresh_cpu_vm_stats(void)
+static int refresh_cpu_vm_stats(bool do_pagesets)
 {
        struct zone *zone;
        int i;
@@ -484,33 +484,35 @@ static int refresh_cpu_vm_stats(void)
 #endif
                        }
                }
-               cond_resched();
 #ifdef CONFIG_NUMA
-               /*
-                * Deal with draining the remote pageset of this
-                * processor
-                *
-                * Check if there are pages remaining in this pageset
-                * if not then there is nothing to expire.
-                */
-               if (!__this_cpu_read(p->expire) ||
+               if (do_pagesets) {
+                       cond_resched();
+                       /*
+                        * Deal with draining the remote pageset of this
+                        * processor
+                        *
+                        * Check if there are pages remaining in this pageset
+                        * if not then there is nothing to expire.
+                        */
+                       if (!__this_cpu_read(p->expire) ||
                               !__this_cpu_read(p->pcp.count))
-                       continue;
+                               continue;
 
-               /*
-                * We never drain zones local to this processor.
-                */
-               if (zone_to_nid(zone) == numa_node_id()) {
-                       __this_cpu_write(p->expire, 0);
-                       continue;
-               }
+                       /*
+                        * We never drain zones local to this processor.
+                        */
+                       if (zone_to_nid(zone) == numa_node_id()) {
+                               __this_cpu_write(p->expire, 0);
+                               continue;
+                       }
 
-               if (__this_cpu_dec_return(p->expire))
-                       continue;
+                       if (__this_cpu_dec_return(p->expire))
+                               continue;
 
-               if (__this_cpu_read(p->pcp.count)) {
-                       drain_zone_pages(zone, this_cpu_ptr(&p->pcp));
-                       changes++;
+                       if (__this_cpu_read(p->pcp.count)) {
+                               drain_zone_pages(zone, this_cpu_ptr(&p->pcp));
+                               changes++;
+                       }
                }
 #endif
        }
@@ -1386,7 +1388,7 @@ static cpumask_var_t cpu_stat_off;
 
 static void vmstat_update(struct work_struct *w)
 {
-       if (refresh_cpu_vm_stats()) {
+       if (refresh_cpu_vm_stats(true)) {
                /*
                 * Counters were updated so we expect more updates
                 * to occur in the future. Keep on running the
@@ -1417,6 +1419,23 @@ 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)
+{
+       if (system_state != SYSTEM_RUNNING)
+               return;
+
+       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(false));
+}
+
 /*
  * Check if the diffs for a certain cpu indicate that
  * an update is needed.
@@ -1449,7 +1468,7 @@ static bool need_update(int cpu)
  */
 static void vmstat_shepherd(struct work_struct *w);
 
-static DECLARE_DELAYED_WORK(shepherd, vmstat_shepherd);
+static DECLARE_DEFERRABLE_WORK(shepherd, vmstat_shepherd);
 
 static void vmstat_shepherd(struct work_struct *w)
 {