mm, vmscan: only allocate and reclaim from zones with pages managed by the buddy allocator

Firmware Assisted Dump (FA_DUMP) on ppc64 reserves substantial amounts
of memory when booting a secondary kernel.  Srikar Dronamraju reported
that multiple nodes may have no memory managed by the buddy allocator
but still return true for populated_zone().

Commit 1d82de618d ("mm, vmscan: make kswapd reclaim in terms of
nodes") was reported to cause kswapd to spin at 100% CPU usage when
fadump was enabled.  The old code happened to deal with the situation of
a populated node with zero free pages by co-incidence but the current
code tries to reclaim populated zones without realising that is
impossible.

We cannot just convert populated_zone() as many existing users really
need to check for present_pages.  This patch introduces a managed_zone()
helper and uses it in the few cases where it is critical that the check
is made for managed pages -- zonelist construction and page reclaim.

Link: http://lkml.kernel.org/r/20160831195104.GB8119@techsingularity.net
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Reported-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Tested-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
Acked-by: Michal Hocko <mhocko@suse.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/mmzone.h

@@ -828,9 +828,21 @@ unsigned long __init node_memmap_size_bytes(int, unsigned long, unsigned long);
  */
 #define zone_idx(zone)		((zone) - (zone)->zone_pgdat->node_zones)
 
-static inline int populated_zone(struct zone *zone)
+/*
+ * Returns true if a zone has pages managed by the buddy allocator.
+ * All the reclaim decisions have to use this function rather than
+ * populated_zone(). If the whole zone is reserved then we can easily
+ * end up with populated_zone() && !managed_zone().
+ */
+static inline bool managed_zone(struct zone *zone)
 {
-	return (!!zone->present_pages);
+	return zone->managed_pages;
+}
+
+/* Returns true if a zone has memory */
+static inline bool populated_zone(struct zone *zone)
+{
+	return zone->present_pages;
 }
 
 extern int movable_zone;

mm/page_alloc.c

@@ -4360,7 +4360,7 @@ static int build_zonelists_node(pg_data_t *pgdat, struct zonelist *zonelist,
 	do {
 		zone_type--;
 		zone = pgdat->node_zones + zone_type;
-		if (populated_zone(zone)) {
+		if (managed_zone(zone)) {
 			zoneref_set_zone(zone,
 				&zonelist->_zonerefs[nr_zones++]);
 			check_highest_zone(zone_type);
@@ -4598,7 +4598,7 @@ static void build_zonelists_in_zone_order(pg_data_t *pgdat, int nr_nodes)
 		for (j = 0; j < nr_nodes; j++) {
 			node = node_order[j];
 			z = &NODE_DATA(node)->node_zones[zone_type];
-			if (populated_zone(z)) {
+			if (managed_zone(z)) {
 				zoneref_set_zone(z,
 					&zonelist->_zonerefs[pos++]);
 				check_highest_zone(zone_type);

mm/vmscan.c

@@ -1665,7 +1665,7 @@ static bool inactive_reclaimable_pages(struct lruvec *lruvec,
 
 	for (zid = sc->reclaim_idx; zid >= 0; zid--) {
 		zone = &pgdat->node_zones[zid];
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		if (zone_page_state_snapshot(zone, NR_ZONE_LRU_BASE +
@@ -2036,7 +2036,7 @@ static bool inactive_list_is_low(struct lruvec *lruvec, bool file,
 		struct zone *zone = &pgdat->node_zones[zid];
 		unsigned long inactive_zone, active_zone;
 
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		inactive_zone = zone_page_state(zone,
@@ -2171,7 +2171,7 @@ static void get_scan_count(struct lruvec *lruvec, struct mem_cgroup *memcg,
 
 		for (z = 0; z < MAX_NR_ZONES; z++) {
 			struct zone *zone = &pgdat->node_zones[z];
-			if (!populated_zone(zone))
+			if (!managed_zone(zone))
 				continue;
 
 			total_high_wmark += high_wmark_pages(zone);
@@ -2510,7 +2510,7 @@ static inline bool should_continue_reclaim(struct pglist_data *pgdat,
 	/* If compaction would go ahead or the allocation would succeed, stop */
 	for (z = 0; z <= sc->reclaim_idx; z++) {
 		struct zone *zone = &pgdat->node_zones[z];
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		switch (compaction_suitable(zone, sc->order, 0, sc->reclaim_idx)) {
@@ -2840,7 +2840,7 @@ static bool pfmemalloc_watermark_ok(pg_data_t *pgdat)
 
 	for (i = 0; i <= ZONE_NORMAL; i++) {
 		zone = &pgdat->node_zones[i];
-		if (!populated_zone(zone) ||
+		if (!managed_zone(zone) ||
 		    pgdat_reclaimable_pages(pgdat) == 0)
 			continue;
 
@@ -3141,7 +3141,7 @@ static bool prepare_kswapd_sleep(pg_data_t *pgdat, int order, int classzone_idx)
 	for (i = 0; i <= classzone_idx; i++) {
 		struct zone *zone = pgdat->node_zones + i;
 
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		if (!zone_balanced(zone, order, classzone_idx))
@@ -3169,7 +3169,7 @@ static bool kswapd_shrink_node(pg_data_t *pgdat,
 	sc->nr_to_reclaim = 0;
 	for (z = 0; z <= sc->reclaim_idx; z++) {
 		zone = pgdat->node_zones + z;
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		sc->nr_to_reclaim += max(high_wmark_pages(zone), SWAP_CLUSTER_MAX);
@@ -3242,7 +3242,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 		if (buffer_heads_over_limit) {
 			for (i = MAX_NR_ZONES - 1; i >= 0; i--) {
 				zone = pgdat->node_zones + i;
-				if (!populated_zone(zone))
+				if (!managed_zone(zone))
 					continue;
 
 				sc.reclaim_idx = i;
@@ -3262,7 +3262,7 @@ static int balance_pgdat(pg_data_t *pgdat, int order, int classzone_idx)
 		 */
 		for (i = classzone_idx; i >= 0; i--) {
 			zone = pgdat->node_zones + i;
-			if (!populated_zone(zone))
+			if (!managed_zone(zone))
 				continue;
 
 			if (zone_balanced(zone, sc.order, classzone_idx))
@@ -3508,7 +3508,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
 	pg_data_t *pgdat;
 	int z;
 
-	if (!populated_zone(zone))
+	if (!managed_zone(zone))
 		return;
 
 	if (!cpuset_zone_allowed(zone, GFP_KERNEL | __GFP_HARDWALL))
@@ -3522,7 +3522,7 @@ void wakeup_kswapd(struct zone *zone, int order, enum zone_type classzone_idx)
 	/* Only wake kswapd if all zones are unbalanced */
 	for (z = 0; z <= classzone_idx; z++) {
 		zone = pgdat->node_zones + z;
-		if (!populated_zone(zone))
+		if (!managed_zone(zone))
 			continue;
 
 		if (zone_balanced(zone, order, classzone_idx))