[PATCH] Use ZVC for inactive and active counts

The determination of the dirty ratio to determine writeback behavior is
currently based on the number of total pages on the system.

However, not all pages in the system may be dirtied.  Thus the ratio is always
too low and can never reach 100%.  The ratio may be particularly skewed if
large hugepage allocations, slab allocations or device driver buffers make
large sections of memory not available anymore.  In that case we may get into
a situation in which f.e.  the background writeback ratio of 40% cannot be
reached anymore which leads to undesired writeback behavior.

This patchset fixes that issue by determining the ratio based on the actual
pages that may potentially be dirty.  These are the pages on the active and
the inactive list plus free pages.

The problem with those counts has so far been that it is expensive to
calculate these because counts from multiple nodes and multiple zones will
have to be summed up.  This patchset makes these counters ZVC counters.  This
means that a current sum per zone, per node and for the whole system is always
available via global variables and not expensive anymore to calculate.

The patchset results in some other good side effects:

- Removal of the various functions that sum up free, active and inactive
  page counts

- Cleanup of the functions that display information via the proc filesystem.

This patch:

The use of a ZVC for nr_inactive and nr_active allows a simplification of some
counter operations.  More ZVC functionality is used for sums etc in the
following patches.

[akpm@osdl.org: UP build fix]
Signed-off-by: Christoph Lameter <clameter@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 28 insertions, 23 deletions

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7430df6..0655d5f 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -679,7 +679,7 @@ static unsigned long shrink_inactive_list(unsigned long max_scan,
 		nr_taken = isolate_lru_pages(sc->swap_cluster_max,
 					     &zone->inactive_list,
 					     &page_list, &nr_scan);
-		zone->nr_inactive -= nr_taken;
+		__mod_zone_page_state(zone, NR_INACTIVE, -nr_taken);
 		zone->pages_scanned += nr_scan;
 		spin_unlock_irq(&zone->lru_lock);
 
@@ -740,7 +740,8 @@ static inline void note_zone_scanning_priority(struct zone *zone, int priority)
 
 static inline int zone_is_near_oom(struct zone *zone)
 {
-	return zone->pages_scanned >= (zone->nr_active + zone->nr_inactive)*3;
+	return zone->pages_scanned >= (zone_page_state(zone, NR_ACTIVE)
+				+ zone_page_state(zone, NR_INACTIVE))*3;
 }
 
 /*
@@ -825,7 +826,7 @@ force_reclaim_mapped:
 	pgmoved = isolate_lru_pages(nr_pages, &zone->active_list,
 				    &l_hold, &pgscanned);
 	zone->pages_scanned += pgscanned;
-	zone->nr_active -= pgmoved;
+	__mod_zone_page_state(zone, NR_ACTIVE, -pgmoved);
 	spin_unlock_irq(&zone->lru_lock);
 
 	while (!list_empty(&l_hold)) {
@@ -857,7 +858,7 @@ force_reclaim_mapped:
 		list_move(&page->lru, &zone->inactive_list);
 		pgmoved++;
 		if (!pagevec_add(&pvec, page)) {
-			zone->nr_inactive += pgmoved;
+			__mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
 			spin_unlock_irq(&zone->lru_lock);
 			pgdeactivate += pgmoved;
 			pgmoved = 0;
@@ -867,7 +868,7 @@ force_reclaim_mapped:
 			spin_lock_irq(&zone->lru_lock);
 		}
 	}
-	zone->nr_inactive += pgmoved;
+	__mod_zone_page_state(zone, NR_INACTIVE, pgmoved);
 	pgdeactivate += pgmoved;
 	if (buffer_heads_over_limit) {
 		spin_unlock_irq(&zone->lru_lock);
@@ -885,14 +886,14 @@ force_reclaim_mapped:
 		list_move(&page->lru, &zone->active_list);
 		pgmoved++;
 		if (!pagevec_add(&pvec, page)) {
-			zone->nr_active += pgmoved;
+			__mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
 			pgmoved = 0;
 			spin_unlock_irq(&zone->lru_lock);
 			__pagevec_release(&pvec);
 			spin_lock_irq(&zone->lru_lock);
 		}
 	}
-	zone->nr_active += pgmoved;
+	__mod_zone_page_state(zone, NR_ACTIVE, pgmoved);
 
 	__count_zone_vm_events(PGREFILL, zone, pgscanned);
 	__count_vm_events(PGDEACTIVATE, pgdeactivate);
@@ -918,14 +919,16 @@ static unsigned long shrink_zone(int priority, struct zone *zone,
 	 * Add one to `nr_to_scan' just to make sure that the kernel will
 	 * slowly sift through the active list.
 	 */
-	zone->nr_scan_active += (zone->nr_active >> priority) + 1;
+	zone->nr_scan_active +=
+		(zone_page_state(zone, NR_ACTIVE) >> priority) + 1;
 	nr_active = zone->nr_scan_active;
 	if (nr_active >= sc->swap_cluster_max)
 		zone->nr_scan_active = 0;
 	else
 		nr_active = 0;
 
-	zone->nr_scan_inactive += (zone->nr_inactive >> priority) + 1;
+	zone->nr_scan_inactive +=
+		(zone_page_state(zone, NR_INACTIVE) >> priority) + 1;
 	nr_inactive = zone->nr_scan_inactive;
 	if (nr_inactive >= sc->swap_cluster_max)
 		zone->nr_scan_inactive = 0;
@@ -1037,7 +1040,8 @@ unsigned long try_to_free_pages(struct zone **zones, gfp_t gfp_mask)
 		if (!cpuset_zone_allowed_hardwall(zone, GFP_KERNEL))
 			continue;
 
-		lru_pages += zone->nr_active + zone->nr_inactive;
+		lru_pages += zone_page_state(zone, NR_ACTIVE)
+				+ zone_page_state(zone, NR_INACTIVE);
 	}
 
 	for (priority = DEF_PRIORITY; priority >= 0; priority--) {
@@ -1182,7 +1186,8 @@ loop_again:
 		for (i = 0; i <= end_zone; i++) {
 			struct zone *zone = pgdat->node_zones + i;
 
-			lru_pages += zone->nr_active + zone->nr_inactive;
+			lru_pages += zone_page_state(zone, NR_ACTIVE)
+					+ zone_page_state(zone, NR_INACTIVE);
 		}
 
 		/*
@@ -1219,8 +1224,9 @@ loop_again:
 			if (zone->all_unreclaimable)
 				continue;
 			if (nr_slab == 0 && zone->pages_scanned >=
-				    (zone->nr_active + zone->nr_inactive) * 6)
-				zone->all_unreclaimable = 1;
+				(zone_page_state(zone, NR_ACTIVE)
+				+ zone_page_state(zone, NR_INACTIVE)) * 6)
+					zone->all_unreclaimable = 1;
 			/*
 			 * If we've done a decent amount of scanning and
 			 * the reclaim ratio is low, start doing writepage
@@ -1385,18 +1391,22 @@ static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
 
 		/* For pass = 0 we don't shrink the active list */
 		if (pass > 0) {
-			zone->nr_scan_active += (zone->nr_active >> prio) + 1;
+			zone->nr_scan_active +=
+				(zone_page_state(zone, NR_ACTIVE) >> prio) + 1;
 			if (zone->nr_scan_active >= nr_pages || pass > 3) {
 				zone->nr_scan_active = 0;
-				nr_to_scan = min(nr_pages, zone->nr_active);
+				nr_to_scan = min(nr_pages,
+					zone_page_state(zone, NR_ACTIVE));
 				shrink_active_list(nr_to_scan, zone, sc, prio);
 			}
 		}
 
-		zone->nr_scan_inactive += (zone->nr_inactive >> prio) + 1;
+		zone->nr_scan_inactive +=
+			(zone_page_state(zone, NR_INACTIVE) >> prio) + 1;
 		if (zone->nr_scan_inactive >= nr_pages || pass > 3) {
 			zone->nr_scan_inactive = 0;
-			nr_to_scan = min(nr_pages, zone->nr_inactive);
+			nr_to_scan = min(nr_pages,
+				zone_page_state(zone, NR_INACTIVE));
 			ret += shrink_inactive_list(nr_to_scan, zone, sc);
 			if (ret >= nr_pages)
 				return ret;
@@ -1408,12 +1418,7 @@ static unsigned long shrink_all_zones(unsigned long nr_pages, int prio,
 
 static unsigned long count_lru_pages(void)
 {
-	struct zone *zone;
-	unsigned long ret = 0;
-
-	for_each_zone(zone)
-		ret += zone->nr_active + zone->nr_inactive;
-	return ret;
+	return global_page_state(NR_ACTIVE) + global_page_state(NR_INACTIVE);
 }
 
 /*