mm: vmscan: clean up struct scan_control

Reorder the members by input and output, then turn the individual
integers for may_writepage, may_unmap, may_swap, compaction_ready,
hibernation_mode into bit fields to save stack space:

  +72/-296 -224
  kswapd                                       104     176     +72
  try_to_free_pages                             80      56     -24
  try_to_free_mem_cgroup_pages                  80      56     -24
  shrink_all_memory                             88      64     -24
  reclaim_clean_pages_from_list                168     144     -24
  mem_cgroup_shrink_node_zone                  104      80     -24
  __zone_reclaim                               176     152     -24
  balance_pgdat                                152       -    -152

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Suggested-by: Mel Gorman <mgorman@suse.de>
Acked-by: Mel Gorman <mgorman@suse.de>
Acked-by: Michal Hocko <mhocko@suse.cz>
Cc: Minchan Kim <minchan.kim@gmail.com>
Cc: Rik van Riel <riel@redhat.com>
Acked-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/vmscan.c

@@ -59,35 +59,20 @@
 #include <trace/events/vmscan.h>
 
 struct scan_control {
-	/* Incremented by the number of inactive pages that were scanned */
-	unsigned long nr_scanned;
-
-	/* Number of pages freed so far during a call to shrink_zones() */
-	unsigned long nr_reclaimed;
-
-	/* One of the zones is ready for compaction */
-	int compaction_ready;
-
 	/* How many pages shrink_list() should reclaim */
 	unsigned long nr_to_reclaim;
 
-	unsigned long hibernation_mode;
-
 	/* This context's GFP mask */
 	gfp_t gfp_mask;
 
-	int may_writepage;
-
-	/* Can mapped pages be reclaimed? */
-	int may_unmap;
-
-	/* Can pages be swapped as part of reclaim? */
-	int may_swap;
-
+	/* Allocation order */
 	int order;
 
-	/* Scan (total_size >> priority) pages at once */
-	int priority;
+	/*
+	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
+	 * are scanned.
+	 */
+	nodemask_t	*nodemask;
 
 	/*
 	 * The memory cgroup that hit its limit and as a result is the
@@ -95,11 +80,27 @@ struct scan_control {
 	 */
 	struct mem_cgroup *target_mem_cgroup;
 
-	/*
-	 * Nodemask of nodes allowed by the caller. If NULL, all nodes
-	 * are scanned.
-	 */
-	nodemask_t	*nodemask;
+	/* Scan (total_size >> priority) pages at once */
+	int priority;
+
+	unsigned int may_writepage:1;
+
+	/* Can mapped pages be reclaimed? */
+	unsigned int may_unmap:1;
+
+	/* Can pages be swapped as part of reclaim? */
+	unsigned int may_swap:1;
+
+	unsigned int hibernation_mode:1;
+
+	/* One of the zones is ready for compaction */
+	unsigned int compaction_ready:1;
+
+	/* Incremented by the number of inactive pages that were scanned */
+	unsigned long nr_scanned;
+
+	/* Number of pages freed so far during a call to shrink_zones() */
+	unsigned long nr_reclaimed;
 };
 
 #define lru_to_page(_head) (list_entry((_head)->prev, struct page, lru))
@@ -2668,15 +2669,14 @@ unsigned long try_to_free_pages(struct zonelist *zonelist, int order,
 {
 	unsigned long nr_reclaimed;
 	struct scan_control sc = {
+		.nr_to_reclaim = SWAP_CLUSTER_MAX,
 		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
+		.order = order,
+		.nodemask = nodemask,
+		.priority = DEF_PRIORITY,
 		.may_writepage = !laptop_mode,
-		.nr_to_reclaim = SWAP_CLUSTER_MAX,
 		.may_unmap = 1,
 		.may_swap = 1,
-		.order = order,
-		.priority = DEF_PRIORITY,
-		.target_mem_cgroup = NULL,
-		.nodemask = nodemask,
 	};
 
 	/*
@@ -2706,14 +2706,11 @@ unsigned long mem_cgroup_shrink_node_zone(struct mem_cgroup *memcg,
 						unsigned long *nr_scanned)
 {
 	struct scan_control sc = {
-		.nr_scanned = 0,
 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
+		.target_mem_cgroup = memcg,
 		.may_writepage = !laptop_mode,
 		.may_unmap = 1,
 		.may_swap = !noswap,
-		.order = 0,
-		.priority = 0,
-		.target_mem_cgroup = memcg,
 	};
 	struct lruvec *lruvec = mem_cgroup_zone_lruvec(zone, memcg);
 	int swappiness = mem_cgroup_swappiness(memcg);
@@ -2748,16 +2745,14 @@ unsigned long try_to_free_mem_cgroup_pages(struct mem_cgroup *memcg,
 	unsigned long nr_reclaimed;
 	int nid;
 	struct scan_control sc = {
-		.may_writepage = !laptop_mode,
-		.may_unmap = 1,
-		.may_swap = !noswap,
 		.nr_to_reclaim = SWAP_CLUSTER_MAX,
-		.order = 0,
-		.priority = DEF_PRIORITY,
-		.target_mem_cgroup = memcg,
-		.nodemask = NULL, /* we don't care the placement */
 		.gfp_mask = (gfp_mask & GFP_RECLAIM_MASK) |
 				(GFP_HIGHUSER_MOVABLE & ~GFP_RECLAIM_MASK),
+		.target_mem_cgroup = memcg,
+		.priority = DEF_PRIORITY,
+		.may_writepage = !laptop_mode,
+		.may_unmap = 1,
+		.may_swap = !noswap,
 	};
 
 	/*
@@ -3015,12 +3010,11 @@ static unsigned long balance_pgdat(pg_data_t *pgdat, int order,
 	unsigned long nr_soft_scanned;
 	struct scan_control sc = {
 		.gfp_mask = GFP_KERNEL,
+		.order = order,
 		.priority = DEF_PRIORITY,
+		.may_writepage = !laptop_mode,
 		.may_unmap = 1,
 		.may_swap = 1,
-		.may_writepage = !laptop_mode,
-		.order = order,
-		.target_mem_cgroup = NULL,
 	};
 	count_vm_event(PAGEOUTRUN);
 
@@ -3401,14 +3395,13 @@ unsigned long shrink_all_memory(unsigned long nr_to_reclaim)
 {
 	struct reclaim_state reclaim_state;
 	struct scan_control sc = {
+		.nr_to_reclaim = nr_to_reclaim,
 		.gfp_mask = GFP_HIGHUSER_MOVABLE,
-		.may_swap = 1,
-		.may_unmap = 1,
+		.priority = DEF_PRIORITY,
 		.may_writepage = 1,
-		.nr_to_reclaim = nr_to_reclaim,
+		.may_unmap = 1,
+		.may_swap = 1,
 		.hibernation_mode = 1,
-		.order = 0,
-		.priority = DEF_PRIORITY,
 	};
 	struct zonelist *zonelist = node_zonelist(numa_node_id(), sc.gfp_mask);
 	struct task_struct *p = current;
@@ -3588,13 +3581,13 @@ static int __zone_reclaim(struct zone *zone, gfp_t gfp_mask, unsigned int order)
 	struct task_struct *p = current;
 	struct reclaim_state reclaim_state;
 	struct scan_control sc = {
-		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
-		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
-		.may_swap = 1,
 		.nr_to_reclaim = max(nr_pages, SWAP_CLUSTER_MAX),
 		.gfp_mask = (gfp_mask = memalloc_noio_flags(gfp_mask)),
 		.order = order,
 		.priority = ZONE_RECLAIM_PRIORITY,
+		.may_writepage = !!(zone_reclaim_mode & RECLAIM_WRITE),
+		.may_unmap = !!(zone_reclaim_mode & RECLAIM_SWAP),
+		.may_swap = 1,
 	};
 	struct shrink_control shrink = {
 		.gfp_mask = sc.gfp_mask,