[PATCH 2/2] mm: page_alloc: Do not cache reclaim distances

[Mel Gorman]

pgdat->reclaim_nodes tracks if a remote node is allowed to be reclaimed by
zone_reclaim due to its distance. As it is expected that zone_reclaim_mode
will be rarely enabled it is unreasonable for all machines to take a penalty.
Fortunately, the zone_reclaim_mode() path is already slow and it is the path
that takes the hit.

Signed-off-by: Mel Gorman <mgorman@xxxxxxx>
---
 include/linux/mmzone.h |  1 -
 mm/page_alloc.c        | 15 +--------------
 2 files changed, 1 insertion(+), 15 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index 9b61b9b..564b169 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -757,7 +757,6 @@ typedef struct pglist_data {
 	unsigned long node_spanned_pages; /* total size of physical page
 					     range, including holes */
 	int node_id;
-	nodemask_t reclaim_nodes;	/* Nodes allowed to reclaim from */
 	wait_queue_head_t kswapd_wait;
 	wait_queue_head_t pfmemalloc_wait;
 	struct task_struct *kswapd;	/* Protected by lock_memory_hotplug() */
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index a256f85..574928e 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1863,16 +1863,7 @@ static bool zone_local(struct zone *local_zone, struct zone *zone)
 
 static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
 {
-	return node_isset(local_zone->node, zone->zone_pgdat->reclaim_nodes);
-}
-
-static void __paginginit init_zone_allows_reclaim(int nid)
-{
-	int i;
-
-	for_each_online_node(i)
-		if (node_distance(nid, i) <= RECLAIM_DISTANCE)
-			node_set(i, NODE_DATA(nid)->reclaim_nodes);
+	return node_distance(zone_to_nid(local_zone), zone_to_nid(zone)) < RECLAIM_DISTANCE;
 }
 
 #else	/* CONFIG_NUMA */
@@ -1906,9 +1897,6 @@ static bool zone_allows_reclaim(struct zone *local_zone, struct zone *zone)
 	return true;
 }
 
-static inline void init_zone_allows_reclaim(int nid)
-{
-}
 #endif	/* CONFIG_NUMA */
 
 /*
@@ -4917,7 +4905,6 @@ void __paginginit free_area_init_node(int nid, unsigned long *zones_size,
 
 	pgdat->node_id = nid;
 	pgdat->node_start_pfn = node_start_pfn;
-	init_zone_allows_reclaim(nid);
 #ifdef CONFIG_HAVE_MEMBLOCK_NODE_MAP
 	get_pfn_range_for_nid(nid, &start_pfn, &end_pfn);
 #endif
-- 
1.8.4.5

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