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Commit 0d5d823a authored by Mel Gorman's avatar Mel Gorman Committed by Linus Torvalds
Browse files

mm: move zone->pages_scanned into a vmstat counter 



zone->pages_scanned is a write-intensive cache line during page reclaim
and it's also updated during page free.  Move the counter into vmstat to
take advantage of the per-cpu updates and do not update it in the free
paths unless necessary.

On a small UMA machine running tiobench the difference is marginal.  On
a 4-node machine the overhead is more noticable.  Note that automatic
NUMA balancing was disabled for this test as otherwise the system CPU
overhead is unpredictable.

          3.16.0-rc3  3.16.0-rc3  3.16.0-rc3
             vanillarearrange-v5   vmstat-v5
User          746.94      759.78      774.56
System      65336.22    58350.98    32847.27
Elapsed     27553.52    27282.02    27415.04

Note that the overhead reduction will vary depending on where exactly
pages are allocated and freed.

Signed-off-by: default avatarMel Gorman <mgorman@suse.de>
Acked-by: default avatarJohannes Weiner <hannes@cmpxchg.org>
Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
parent 3484b2de

include/linux/mmzone.h

+1 −1
Original line number Diff line number Diff line
@@ -143,6 +143,7 @@ enum zone_stat_item { 
	NR_SHMEM,		/* shmem pages (included tmpfs/GEM pages) */

	NR_DIRTIED,		/* page dirtyings since bootup */

	NR_WRITTEN,		/* page writings since bootup */

	NR_PAGES_SCANNED,	/* pages scanned since last reclaim */

#ifdef CONFIG_NUMA

	NUMA_HIT,		/* allocated in intended node */

	NUMA_MISS,		/* allocated in non intended node */
@@ -480,7 +481,6 @@ struct zone { 


	/* Fields commonly accessed by the page reclaim scanner */

	spinlock_t		lru_lock;

	unsigned long		pages_scanned;	   /* since last reclaim */

	struct lruvec		lruvec;



	/* Evictions & activations on the inactive file list */

mm/page_alloc.c

+9 −3
Original line number Diff line number Diff line
@@ -680,9 +680,12 @@ static void free_pcppages_bulk(struct zone *zone, int count, 
	int migratetype = 0;

	int batch_free = 0;

	int to_free = count;

	unsigned long nr_scanned;



	spin_lock(&zone->lock);

	zone->pages_scanned = 0;

	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);

	if (nr_scanned)

		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);



	while (to_free) {

		struct page *page;
@@ -731,8 +734,11 @@ static void free_one_page(struct zone *zone, 
				unsigned int order,

				int migratetype)

{

	unsigned long nr_scanned;

	spin_lock(&zone->lock);

	zone->pages_scanned = 0;

	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);

	if (nr_scanned)

		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);



	__free_one_page(page, pfn, zone, order, migratetype);

	if (unlikely(!is_migrate_isolate(migratetype)))
@@ -3248,7 +3254,7 @@ void show_free_areas(unsigned int filter) 
			K(zone_page_state(zone, NR_BOUNCE)),

			K(zone_page_state(zone, NR_FREE_CMA_PAGES)),

			K(zone_page_state(zone, NR_WRITEBACK_TEMP)),

			zone->pages_scanned,

			K(zone_page_state(zone, NR_PAGES_SCANNED)),

			(!zone_reclaimable(zone) ? "yes" : "no")

			);

		printk("lowmem_reserve[]:");

mm/vmscan.c

+4 −3
Original line number Diff line number Diff line
@@ -174,7 +174,8 @@ static unsigned long zone_reclaimable_pages(struct zone *zone) 


bool zone_reclaimable(struct zone *zone)

{

	return zone->pages_scanned < zone_reclaimable_pages(zone) * 6;

	return zone_page_state(zone, NR_PAGES_SCANNED) <

		zone_reclaimable_pages(zone) * 6;

}



static unsigned long get_lru_size(struct lruvec *lruvec, enum lru_list lru)
@@ -1508,7 +1509,7 @@ shrink_inactive_list(unsigned long nr_to_scan, struct lruvec *lruvec, 
	__mod_zone_page_state(zone, NR_ISOLATED_ANON + file, nr_taken);



	if (global_reclaim(sc)) {

		zone->pages_scanned += nr_scanned;

		__mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);

		if (current_is_kswapd())

			__count_zone_vm_events(PGSCAN_KSWAPD, zone, nr_scanned);

		else
@@ -1698,7 +1699,7 @@ static void shrink_active_list(unsigned long nr_to_scan, 
	nr_taken = isolate_lru_pages(nr_to_scan, lruvec, &l_hold,

				     &nr_scanned, sc, isolate_mode, lru);

	if (global_reclaim(sc))

		zone->pages_scanned += nr_scanned;

		__mod_zone_page_state(zone, NR_PAGES_SCANNED, nr_scanned);



	reclaim_stat->recent_scanned[file] += nr_taken;

mm/vmstat.c

+2 −1
Original line number Diff line number Diff line
@@ -763,6 +763,7 @@ const char * const vmstat_text[] = { 
	"nr_shmem",

	"nr_dirtied",

	"nr_written",

	"nr_pages_scanned",



#ifdef CONFIG_NUMA

	"numa_hit",
@@ -1067,7 +1068,7 @@ 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),

		   zone->pages_scanned,

		   zone_page_state(zone, NR_PAGES_SCANNED),

		   zone->spanned_pages,

		   zone->present_pages,

		   zone->managed_pages);