[PATCH 7/9] mm: delete NR_PAGES_SCANNED and pgdat_reclaimable()

[Johannes Weiner <hannes@cmpxchg.org>]

NR_PAGES_SCANNED counts number of pages scanned since the last page
free event in the allocator. This was used primarily to measure the
reclaimability of zones and nodes, and determine when reclaim should
give up on them. In that role, it has been replaced in the preceeding
patches by a different mechanism.

Being implemented as an efficient vmstat counter, it was automatically
exported to userspace as well. It's however unlikely that anyone
outside the kernel is using this counter in any meaningful way.

Remove the counter and the unused pgdat_reclaimable().

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
---
 include/linux/mmzone.h |  1 -
 mm/internal.h          |  1 -
 mm/page_alloc.c        | 15 +++------------
 mm/vmscan.c            |  9 ---------
 mm/vmstat.c            | 22 +++-------------------
 5 files changed, 6 insertions(+), 42 deletions(-)

diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
index d2c50ab6ae40..04e0969966f6 100644
--- a/include/linux/mmzone.h
+++ b/include/linux/mmzone.h
@@ -149,7 +149,6 @@ enum node_stat_item {
 	NR_UNEVICTABLE,		/*  "     "     "   "       "         */
 	NR_ISOLATED_ANON,	/* Temporary isolated pages from anon lru */
 	NR_ISOLATED_FILE,	/* Temporary isolated pages from file lru */
-	NR_PAGES_SCANNED,	/* pages scanned since last reclaim */
 	WORKINGSET_REFAULT,
 	WORKINGSET_ACTIVATE,
 	WORKINGSET_NODERECLAIM,
diff --git a/mm/internal.h b/mm/internal.h
index aae93e3fd984..c583ce1b32b9 100644
--- a/mm/internal.h
+++ b/mm/internal.h
@@ -91,7 +91,6 @@ extern unsigned long highest_memmap_pfn;
  */
 extern int isolate_lru_page(struct page *page);
 extern void putback_lru_page(struct page *page);
-extern bool pgdat_reclaimable(struct pglist_data *pgdat);
 
 /*
  * in mm/rmap.c:
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index f50e36e7b024..9ac639864bed 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -1088,15 +1088,11 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 {
 	int migratetype = 0;
 	int batch_free = 0;
-	unsigned long nr_scanned, flags;
+	unsigned long flags;
 	bool isolated_pageblocks;
 
 	spin_lock_irqsave(&zone->lock, flags);
 	isolated_pageblocks = has_isolate_pageblock(zone);
-	nr_scanned = node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED);
-	if (nr_scanned)
-		__mod_node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED, -nr_scanned);
-
 	while (count) {
 		struct page *page;
 		struct list_head *list;
@@ -1148,13 +1144,10 @@ static void free_one_page(struct zone *zone,
 				unsigned int order,
 				int migratetype)
 {
-	unsigned long nr_scanned, flags;
+	unsigned long flags;
+
 	spin_lock_irqsave(&zone->lock, flags);
 	__count_vm_events(PGFREE, 1 << order);
-	nr_scanned = node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED);
-	if (nr_scanned)
-		__mod_node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED, -nr_scanned);
-
 	if (unlikely(has_isolate_pageblock(zone) ||
 		is_migrate_isolate(migratetype))) {
 		migratetype = get_pfnblock_migratetype(page, pfn);
@@ -4497,7 +4490,6 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 #endif
 			" writeback_tmp:%lukB"
 			" unstable:%lukB"
-			" pages_scanned:%lu"
 			" all_unreclaimable? %s"
 			"\n",
 			pgdat->node_id,
@@ -4520,7 +4512,6 @@ void show_free_areas(unsigned int filter, nodemask_t *nodemask)
 			K(node_page_state(pgdat, NR_SHMEM)),
 			K(node_page_state(pgdat, NR_WRITEBACK_TEMP)),
 			K(node_page_state(pgdat, NR_UNSTABLE_NFS)),
-			node_page_state(pgdat, NR_PAGES_SCANNED),
 			pgdat->kswapd_failures >= MAX_RECLAIM_RETRIES ?
 				"yes" : "no");
 	}
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 8cff6e2cd02c..35b791a8922b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -229,12 +229,6 @@ unsigned long pgdat_reclaimable_pages(struct pglist_data *pgdat)
 	return nr;
 }
 
-bool pgdat_reclaimable(struct pglist_data *pgdat)
-{
-	return node_page_state_snapshot(pgdat, NR_PAGES_SCANNED) <
-		pgdat_reclaimable_pages(pgdat) * 6;
-}
-
 /**
  * lruvec_lru_size -  Returns the number of pages on the given LRU list.
  * @lruvec: lru vector
@@ -1749,7 +1743,6 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec,
 	reclaim_stat->recent_scanned[file] += nr_taken;
 
 	if (global_reclaim(sc)) {
-		__mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
 		if (current_is_kswapd())
 			__count_vm_events(PGSCAN_KSWAPD, nr_scanned);
 		else
@@ -1952,8 +1945,6 @@ static void shrink_active_list(unsigned long nr_to_scan,
 	__mod_node_page_state(pgdat, NR_ISOLATED_ANON + file, nr_taken);
 	reclaim_stat->recent_scanned[file] += nr_taken;
 
-	if (global_reclaim(sc))
-		__mod_node_page_state(pgdat, NR_PAGES_SCANNED, nr_scanned);
 	__count_vm_events(PGREFILL, nr_scanned);
 
 	spin_unlock_irq(&pgdat->lru_lock);
diff --git a/mm/vmstat.c b/mm/vmstat.c
index ff16cdc15df2..eface7467ea5 100644
--- a/mm/vmstat.c
+++ b/mm/vmstat.c
@@ -954,7 +954,6 @@ const char * const vmstat_text[] = {
 	"nr_unevictable",
 	"nr_isolated_anon",
 	"nr_isolated_file",
-	"nr_pages_scanned",
 	"workingset_refault",
 	"workingset_activate",
 	"workingset_nodereclaim",
@@ -1375,7 +1374,6 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   "\n        min      %lu"
 		   "\n        low      %lu"
 		   "\n        high     %lu"
-		   "\n   node_scanned  %lu"
 		   "\n        spanned  %lu"
 		   "\n        present  %lu"
 		   "\n        managed  %lu",
@@ -1383,7 +1381,6 @@ static void zoneinfo_show_print(struct seq_file *m, pg_data_t *pgdat,
 		   min_wmark_pages(zone),
 		   low_wmark_pages(zone),
 		   high_wmark_pages(zone),
-		   node_page_state(zone->zone_pgdat, NR_PAGES_SCANNED),
 		   zone->spanned_pages,
 		   zone->present_pages,
 		   zone->managed_pages);
@@ -1584,22 +1581,9 @@ int vmstat_refresh(struct ctl_table *table, int write,
 	for (i = 0; i < NR_VM_ZONE_STAT_ITEMS; i++) {
 		val = atomic_long_read(&vm_zone_stat[i]);
 		if (val < 0) {
-			switch (i) {
-			case NR_PAGES_SCANNED:
-				/*
-				 * This is often seen to go negative in
-				 * recent kernels, but not to go permanently
-				 * negative.  Whilst it would be nicer not to
-				 * have exceptions, rooting them out would be
-				 * another task, of rather low priority.
-				 */
-				break;
-			default:
-				pr_warn("%s: %s %ld\n",
-					__func__, vmstat_text[i], val);
-				err = -EINVAL;
-				break;
-			}
+			pr_warn("%s: %s %ld\n",
+				__func__, vmstat_text[i], val);
+			err = -EINVAL;
 		}
 	}
 	if (err)
-- 
2.11.1