[PATCH RFC] mm: reset pages_scanned only when free pages are above high watermark

[Konstantin Khlebnikov <khlebnikov@yandex-team.ru>]

Technically, this counter works as OOM-countdown. Let's reset it only
when zone is completely recovered and ready to handle any allocations.
Otherwise system could never recover and stuck in livelock.

Signed-off-by: Konstantin Khlebnikov <khlebnikov@yandex-team.ru>
---
 mm/page_alloc.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ffd5ad2a6e10..ef7795c8c121 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -701,7 +701,8 @@ static void free_pcppages_bulk(struct zone *zone, int count,
 
 	spin_lock(&zone->lock);
 	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);
-	if (nr_scanned)
+	if (nr_scanned &&
+	    zone_page_state(zone, NR_FREE_PAGES) > high_wmark_pages(zone))
 		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);
 
 	while (to_free) {
@@ -752,7 +753,8 @@ static void free_one_page(struct zone *zone,
 	unsigned long nr_scanned;
 	spin_lock(&zone->lock);
 	nr_scanned = zone_page_state(zone, NR_PAGES_SCANNED);
-	if (nr_scanned)
+	if (nr_scanned &&
+	    zone_page_state(zone, NR_FREE_PAGES) > high_wmark_pages(zone))
 		__mod_zone_page_state(zone, NR_PAGES_SCANNED, -nr_scanned);
 
 	if (unlikely(has_isolate_pageblock(zone) ||