1 files changed, 21 insertions, 0 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 */