[PATCH 3/4] lumpy ensure we respect zone boundaries

[Andy Whitcroft]

lumpy: ensure we respect zone boundaries

When scanning an aligned order N area ensure we only pull out pages
in the same zone as our tag page, else we will manipulate those
pages' LRU under the wrong zone lru_lock.  Bad.

Signed-off-by: Andy Whitcroft <apw@xxxxxxxxxxxx>
Acked-by: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
---
diff --git a/mm/vmscan.c b/mm/vmscan.c
index 0effa3e..85f626b 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -660,6 +660,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 	struct page *page, *tmp;
 	unsigned long scan, pfn, end_pfn, page_pfn;
 	int active;
+	int zone_id;
 
 	for (scan = 0; scan < nr_to_scan && !list_empty(src); scan++) {
 		page = lru_to_page(src);
@@ -691,6 +692,7 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 		 * surrounding the tag page.  Only take those pages of
 		 * the same active state as that tag page.
 		 */
+		zone_id = page_zone_id(page);
 		page_pfn = __page_to_pfn(page);
 		pfn = page_pfn & ~((1 << order) - 1);
 		end_pfn = pfn + (1 << order);
@@ -700,8 +702,10 @@ static unsigned long isolate_lru_pages(unsigned long nr_to_scan,
 			if (unlikely(!pfn_valid(pfn)))
 				break;
 
-			scan++;
 			tmp = __pfn_to_page(pfn);
+			if (unlikely(page_zone_id(tmp) != zone_id))
+				continue;
+			scan++;
 			switch (__isolate_lru_page(tmp, active)) {
 			case 0:
 				list_move(&tmp->lru, dst);
-
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