1 files changed, 49 insertions, 9 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 3584067800e1..d3488828331a 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -2198,10 +2198,40 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *mem_cont,
 }
 #endif
 
+/*
+ * pgdat_balanced is used when checking if a node is balanced for high-order
+ * allocations. Only zones that meet watermarks and are in a zone allowed
+ * by the callers classzone_idx are added to balanced_pages. The total of
+ * balanced pages must be at least 25% of the zones allowed by classzone_idx
+ * for the node to be considered balanced. Forcing all zones to be balanced
+ * for high orders can cause excessive reclaim when there are imbalanced zones.
+ * The choice of 25% is due to
+ *   o a 16M DMA zone that is balanced will not balance a zone on any
+ *     reasonable sized machine
+ *   o On all other machines, the top zone must be at least a reasonable
+ *     precentage of the middle zones. For example, on 32-bit x86, highmem
+ *     would need to be at least 256M for it to be balance a whole node.
+ *     Similarly, on x86-64 the Normal zone would need to be at least 1G
+ *     to balance a node on its own. These seemed like reasonable ratios.
+ */
+static bool pgdat_balanced(pg_data_t *pgdat, unsigned long balanced_pages,
+                                                int classzone_idx)
+{
+        unsigned long present_pages = 0;
+        int i;
+
+        for (i = 0; i <= classzone_idx; i++)
+                present_pages += pgdat->node_zones[i].present_pages;
+
+        return balanced_pages > (present_pages >> 2);
+}
+
 /* is kswapd sleeping prematurely? */
 static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
 {
         int i;
+        unsigned long balanced = 0;
+        bool all_zones_ok = true;
 
         /* If a direct reclaimer woke kswapd within HZ/10, it's premature */
         if (remaining)
@@ -2219,10 +2249,20 @@ static int sleeping_prematurely(pg_data_t *pgdat, int order, long remaining)
 
                 if (!zone_watermark_ok_safe(zone, order, high_wmark_pages(zone),
                                                                 0, 0))
-                        return 1;
+                        all_zones_ok = false;
+                else
+                        balanced += zone->present_pages;
         }
 
-        return 0;
+        /*
+         * For high-order requests, the balanced zones must contain at least
+         * 25% of the nodes pages for kswapd to sleep. For order-0, all zones
+         * must be balanced
+         */
+        if (order)
+                return pgdat_balanced(pgdat, balanced, 0);
+        else
+                return !all_zones_ok;
 }
 
 /*
@@ -2250,7 +2290,7 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
                                                         int classzone_idx)
 {
         int all_zones_ok;
-        int any_zone_ok;
+        unsigned long balanced;
         int priority;
         int i;
         int end_zone = 0;       /* Inclusive.  0 = ZONE_DMA */
@@ -2284,7 +2324,7 @@ loop_again:
                         disable_swap_token();
 
                 all_zones_ok = 1;
-                any_zone_ok = 0;
+                balanced = 0;
 
                 /*
                  * Scan in the highmem->dma direction for the highest
@@ -2404,11 +2444,11 @@ loop_again:
                                  */
                                 zone_clear_flag(zone, ZONE_CONGESTED);
                                 if (i <= classzone_idx)
-                                        any_zone_ok = 1;
+                                        balanced += zone->present_pages;
                         }
 
                 }
-                if (all_zones_ok || (order && any_zone_ok))
+                if (all_zones_ok || (order && pgdat_balanced(pgdat, balanced, classzone_idx)))
                         break;          /* kswapd: all done */
                 /*
                  * OK, kswapd is getting into trouble.  Take a nap, then take
@@ -2434,10 +2474,10 @@ out:
 
         /*
          * order-0: All zones must meet high watermark for a balanced node
-         * high-order: Any zone below pgdats classzone_idx must meet the high
-         *             watermark for a balanced node
+         * high-order: Balanced zones must make up at least 25% of the node
+         *             for the node to be balanced
          */
-        if (!(all_zones_ok || (order && any_zone_ok))) {
+        if (!(all_zones_ok || (order && pgdat_balanced(pgdat, balanced, classzone_idx)))) {
                 cond_resched();
 
                 try_to_freeze();