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>

1 files changed, 44 insertions, 25 deletions

diff --git a/mm/vmstat.c b/mm/vmstat.c
index c54fd2924f25..83a003bc3cae 100644
--- 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
@@ -1418,6 +1420,23 @@ 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)
 {