---

yaml
---
r: 230735
b: refs/heads/master
c: 1741c87
h: refs/heads/master
i:
  230733: 703f999
  230731: 15e2ea8
  230727: 95fbad2
  230719: fdd8e45
v: v3

[refs]

@@ -1,2 +1,2 @@
 ---
-refs/heads/master: 9950474883e027e6e728cbcff25f7f2bf0c96530
+refs/heads/master: 1741c87757448cedd03224f01586504f9256415d

trunk/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 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 			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 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 				 */
 				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 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 
 	/*
 	 * 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();