[PATCH 1/5] mm, vmscan: Do not account skipped pages as scanned

[Mel Gorman <mgorman@techsingularity.net>]

Page reclaim determines whether a pgdat is unreclaimable by examining how
many pages have been scanned since a page was freed and comparing that
to the LRU sizes. Skipped pages are not considered reclaim candidates but
contribute to scanned. This can prematurely mark a pgdat as unreclaimable
and trigger an OOM kill.

While this does not fix an OOM kill message reported by Joonsoo Kim,
it did stop pgdat being marked unreclaimable.

Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
 mm/vmscan.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 22aec2bcfeec..b16d578ce556 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1415,7 +1415,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	LIST_HEAD(pages_skipped);
 
 	for (scan = 0; scan < nr_to_scan && nr_taken < nr_to_scan &&
-					!list_empty(src); scan++) {
+					!list_empty(src);) {
 		struct page *page;
 
 		page = lru_to_page(src);
@@ -1429,6 +1429,9 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			continue;
 		}
 
+		/* Pages skipped do not contribute to scan */
+		scan++;
+
 		switch (__isolate_lru_page(page, mode)) {
 		case 0:
 			nr_pages = hpage_nr_pages(page);
-- 
2.6.4

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