1 files changed, 67 insertions, 1 deletions

diff --git a/mm/vmstat.c b/mm/vmstat.c
index 355a9e669aaa..4d7faebb9b70 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -81,6 +81,30 @@ EXPORT_SYMBOL(vm_stat);
 
 #ifdef CONFIG_SMP
 
+static int calculate_pressure_threshold(struct zone *zone)
+{
+        int threshold;
+        int watermark_distance;
+
+        /*
+         * As vmstats are not up to date, there is drift between the estimated
+         * and real values. For high thresholds and a high number of CPUs, it
+         * is possible for the min watermark to be breached while the estimated
+         * value looks fine. The pressure threshold is a reduced value such
+         * that even the maximum amount of drift will not accidentally breach
+         * the min watermark
+         */
+        watermark_distance = low_wmark_pages(zone) - min_wmark_pages(zone);
+        threshold = max(1, (int)(watermark_distance / num_online_cpus()));
+
+        /*
+         * Maximum threshold is 125
+         */
+        threshold = min(125, threshold);
+
+        return threshold;
+}
+
 static int calculate_threshold(struct zone *zone)
 {
         int threshold;
@@ -159,6 +183,48 @@ static void refresh_zone_stat_thresholds(void)
         }
 }
 
+void reduce_pgdat_percpu_threshold(pg_data_t *pgdat)
+{
+        struct zone *zone;
+        int cpu;
+        int threshold;
+        int i;
+
+        get_online_cpus();
+        for (i = 0; i < pgdat->nr_zones; i++) {
+                zone = &pgdat->node_zones[i];
+                if (!zone->percpu_drift_mark)
+                        continue;
+
+                threshold = calculate_pressure_threshold(zone);
+                for_each_online_cpu(cpu)
+                        per_cpu_ptr(zone->pageset, cpu)->stat_threshold
+                                                        = threshold;
+        }
+        put_online_cpus();
+}
+
+void restore_pgdat_percpu_threshold(pg_data_t *pgdat)
+{
+        struct zone *zone;
+        int cpu;
+        int threshold;
+        int i;
+
+        get_online_cpus();
+        for (i = 0; i < pgdat->nr_zones; i++) {
+                zone = &pgdat->node_zones[i];
+                if (!zone->percpu_drift_mark)
+                        continue;
+
+                threshold = calculate_threshold(zone);
+                for_each_online_cpu(cpu)
+                        per_cpu_ptr(zone->pageset, cpu)->stat_threshold
+                                                        = threshold;
+        }
+        put_online_cpus();
+}
+
 /*
  * For use when we know that interrupts are disabled.
  */
@@ -826,7 +892,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
                    "\n        scanned  %lu"
                    "\n        spanned  %lu"
                    "\n        present  %lu",
-                   zone_nr_free_pages(zone),
+                   zone_page_state(zone, NR_FREE_PAGES),
                    min_wmark_pages(zone),
                    low_wmark_pages(zone),
                    high_wmark_pages(zone),