3 files changed, 37 insertions, 3 deletions

diff --git a/mm/mmzone.c b/mm/mmzone.c
index f5b7d1760213..e35bfb82c855 100644
--- a/mm/mmzone.c
+++ b/mm/mmzone.c
@@ -87,3 +87,24 @@ int memmap_valid_within(unsigned long pfn,
         return 1;
 }
 #endif /* CONFIG_ARCH_HAS_HOLES_MEMORYMODEL */
+
+#ifdef CONFIG_SMP
+/* Called when a more accurate view of NR_FREE_PAGES is needed */
+unsigned long zone_nr_free_pages(struct zone *zone)
+{
+        unsigned long nr_free_pages = zone_page_state(zone, NR_FREE_PAGES);
+
+        /*
+         * While kswapd is awake, it is considered the zone is under some
+         * memory pressure. Under pressure, there is a risk that
+         * per-cpu-counter-drift will allow the min watermark to be breached
+         * potentially causing a live-lock. While kswapd is awake and
+         * free pages are low, get a better estimate for free pages
+         */
+        if (nr_free_pages < zone->percpu_drift_mark &&
+                        !waitqueue_active(&zone->zone_pgdat->kswapd_wait))
+                return zone_page_state_snapshot(zone, NR_FREE_PAGES);
+
+        return nr_free_pages;
+}
+#endif /* CONFIG_SMP */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 452e2ba06c7c..b2d21e06d45d 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1462,7 +1462,7 @@ int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
 {
         /* free_pages my go negative - that's OK */
         long min = mark;
-        long free_pages = zone_page_state(z, NR_FREE_PAGES) - (1 << order) + 1;
+        long free_pages = zone_nr_free_pages(z) - (1 << order) + 1;
         int o;
 
         if (alloc_flags & ALLOC_HIGH)
@@ -2424,7 +2424,7 @@ void show_free_areas(void)
                         " all_unreclaimable? %s"
                         "\n",
                         zone->name,
-                        K(zone_page_state(zone, NR_FREE_PAGES)),
+                        K(zone_nr_free_pages(zone)),
                         K(min_wmark_pages(zone)),
                         K(low_wmark_pages(zone)),
                         K(high_wmark_pages(zone)),
diff --git a/mm/vmstat.c b/mm/vmstat.c
index a8d6b59e609a..355a9e669aaa 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -138,11 +138,24 @@ static void refresh_zone_stat_thresholds(void)
         int threshold;
 
         for_each_populated_zone(zone) {
+                unsigned long max_drift, tolerate_drift;
+
                 threshold = calculate_threshold(zone);
 
                 for_each_online_cpu(cpu)
                         per_cpu_ptr(zone->pageset, cpu)->stat_threshold
                                                         = threshold;
+
+                /*
+                 * Only set percpu_drift_mark if there is a danger that
+                 * NR_FREE_PAGES reports the low watermark is ok when in fact
+                 * the min watermark could be breached by an allocation
+                 */
+                tolerate_drift = low_wmark_pages(zone) - min_wmark_pages(zone);
+                max_drift = num_online_cpus() * threshold;
+                if (max_drift > tolerate_drift)
+                        zone->percpu_drift_mark = high_wmark_pages(zone) +
+                                        max_drift;
         }
 }
 
@@ -813,7 +826,7 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
                    "\n        scanned  %lu"
                    "\n        spanned  %lu"
                    "\n        present  %lu",
-                   zone_page_state(zone, NR_FREE_PAGES),
+                   zone_nr_free_pages(zone),
                    min_wmark_pages(zone),
                    low_wmark_pages(zone),
                    high_wmark_pages(zone),