[PATCH 61 of 66] use compaction for GFP_ATOMIC order > 0

[Andrea Arcangeli]

From: Andrea Arcangeli <aarcange@xxxxxxxxxx>

This takes advantage of memory compaction to properly generate pages of order >
0 if regular page reclaim fails and priority level becomes more severe and we
don't reach the proper watermarks.

Signed-off-by: Andrea Arcangeli <aarcange@xxxxxxxxxx>
---

diff --git a/include/linux/compaction.h b/include/linux/compaction.h
--- a/include/linux/compaction.h
+++ b/include/linux/compaction.h
@@ -11,6 +11,9 @@
 /* The full zone was compacted */
 #define COMPACT_COMPLETE	3
 
+#define COMPACT_MODE_DIRECT_RECLAIM	0
+#define COMPACT_MODE_KSWAPD		1
+
 #ifdef CONFIG_COMPACTION
 extern int sysctl_compact_memory;
 extern int sysctl_compaction_handler(struct ctl_table *table, int write,
@@ -20,6 +23,9 @@ extern int sysctl_extfrag_handler(struct
 			void __user *buffer, size_t *length, loff_t *ppos);
 
 extern int fragmentation_index(struct zone *zone, unsigned int order);
+extern unsigned long compact_zone_order(struct zone *zone,
+					int order, gfp_t gfp_mask,
+					int compact_mode);
 extern unsigned long try_to_compact_pages(struct zonelist *zonelist,
 			int order, gfp_t gfp_mask, nodemask_t *mask);
 
@@ -59,6 +65,13 @@ static inline unsigned long try_to_compa
 	return COMPACT_CONTINUE;
 }
 
+static inline unsigned long compact_zone_order(struct zone *zone,
+					       int order, gfp_t gfp_mask,
+					       int compact_mode)
+{
+	return COMPACT_CONTINUE;
+}
+
 static inline void defer_compaction(struct zone *zone)
 {
 }
diff --git a/mm/compaction.c b/mm/compaction.c
--- a/mm/compaction.c
+++ b/mm/compaction.c
@@ -38,6 +38,8 @@ struct compact_control {
 	unsigned int order;		/* order a direct compactor needs */
 	int migratetype;		/* MOVABLE, RECLAIMABLE etc */
 	struct zone *zone;
+
+	int compact_mode;
 };
 
 static unsigned long release_freepages(struct list_head *freelist)
@@ -357,10 +359,10 @@ static void update_nr_listpages(struct c
 }
 
 static int compact_finished(struct zone *zone,
-						struct compact_control *cc)
+			    struct compact_control *cc)
 {
 	unsigned int order;
-	unsigned long watermark = low_wmark_pages(zone) + (1 << cc->order);
+	unsigned long watermark;
 
 	if (fatal_signal_pending(current))
 		return COMPACT_PARTIAL;
@@ -370,12 +372,27 @@ static int compact_finished(struct zone 
 		return COMPACT_COMPLETE;
 
 	/* Compaction run is not finished if the watermark is not met */
+	if (cc->compact_mode != COMPACT_MODE_KSWAPD)
+		watermark = low_wmark_pages(zone);
+	else
+		watermark = high_wmark_pages(zone);
+	watermark += (1 << cc->order);
+
 	if (!zone_watermark_ok(zone, cc->order, watermark, 0, 0))
 		return COMPACT_CONTINUE;
 
 	if (cc->order == -1)
 		return COMPACT_CONTINUE;
 
+	/*
+	 * Generating only one page of the right order is not enough
+	 * for kswapd, we must continue until we're above the high
+	 * watermark as a pool for high order GFP_ATOMIC allocations
+	 * too.
+	 */
+	if (cc->compact_mode == COMPACT_MODE_KSWAPD)
+		return COMPACT_CONTINUE;
+
 	/* Direct compactor: Is a suitable page free? */
 	for (order = cc->order; order < MAX_ORDER; order++) {
 		/* Job done if page is free of the right migratetype */
@@ -433,8 +450,9 @@ static int compact_zone(struct zone *zon
 	return ret;
 }
 
-static unsigned long compact_zone_order(struct zone *zone,
-						int order, gfp_t gfp_mask)
+unsigned long compact_zone_order(struct zone *zone,
+				 int order, gfp_t gfp_mask,
+				 int compact_mode)
 {
 	struct compact_control cc = {
 		.nr_freepages = 0,
@@ -442,6 +460,7 @@ static unsigned long compact_zone_order(
 		.order = order,
 		.migratetype = allocflags_to_migratetype(gfp_mask),
 		.zone = zone,
+		.compact_mode = compact_mode,
 	};
 	INIT_LIST_HEAD(&cc.freepages);
 	INIT_LIST_HEAD(&cc.migratepages);
@@ -476,7 +495,7 @@ unsigned long try_to_compact_pages(struc
 	 * made because an assumption is made that the page allocator can satisfy
 	 * the "cheaper" orders without taking special steps
 	 */
-	if (order <= PAGE_ALLOC_COSTLY_ORDER || !may_enter_fs || !may_perform_io)
+	if (!order || !may_enter_fs || !may_perform_io)
 		return rc;
 
 	count_vm_event(COMPACTSTALL);
@@ -517,7 +536,8 @@ unsigned long try_to_compact_pages(struc
 			break;
 		}
 
-		status = compact_zone_order(zone, order, gfp_mask);
+		status = compact_zone_order(zone, order, gfp_mask,
+					    COMPACT_MODE_DIRECT_RECLAIM);
 		rc = max(status, rc);
 
 		if (zone_watermark_ok(zone, order, watermark, 0, 0))
@@ -547,6 +567,7 @@ static int compact_node(int nid)
 			.nr_freepages = 0,
 			.nr_migratepages = 0,
 			.order = -1,
+			.compact_mode = COMPACT_MODE_DIRECT_RECLAIM,
 		};
 
 		zone = &pgdat->node_zones[zoneid];
diff --git a/mm/vmscan.c b/mm/vmscan.c
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -40,6 +40,7 @@
 #include <linux/memcontrol.h>
 #include <linux/delayacct.h>
 #include <linux/sysctl.h>
+#include <linux/compaction.h>
 
 #include <asm/tlbflush.h>
 #include <asm/div64.h>
@@ -2254,6 +2255,7 @@ loop_again:
 		 * cause too much scanning of the lower zones.
 		 */
 		for (i = 0; i <= end_zone; i++) {
+			int compaction;
 			struct zone *zone = pgdat->node_zones + i;
 			int nr_slab;
 
@@ -2283,9 +2285,26 @@ loop_again:
 						lru_pages);
 			sc.nr_reclaimed += reclaim_state->reclaimed_slab;
 			total_scanned += sc.nr_scanned;
+
+			compaction = 0;
+			if (order &&
+			    zone_watermark_ok(zone, 0,
+					       high_wmark_pages(zone),
+					      end_zone, 0) &&
+			    !zone_watermark_ok(zone, order,
+					       high_wmark_pages(zone),
+					       end_zone, 0)) {
+				compact_zone_order(zone,
+						   order,
+						   sc.gfp_mask,
+						   COMPACT_MODE_KSWAPD);
+				compaction = 1;
+			}
+
 			if (zone->all_unreclaimable)
 				continue;
-			if (nr_slab == 0 && !zone_reclaimable(zone))
+			if (!compaction && nr_slab == 0 &&
+			    !zone_reclaimable(zone))
 				zone->all_unreclaimable = 1;
 			/*
 			 * If we've done a decent amount of scanning and
--
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