mm/swap.c: clear PageActive before adding pages onto unevictable list

As a result of commit 13f7f789 ("mm: pagevec: defer deciding which
LRU to add a page to until pagevec drain time"), pages on unevictable
lists can have both of PageActive and PageUnevictable set.  This is not
only confusing, but also corrupts page migration and
shrink_[in]active_list.

This patch fixes the problem by adding ClearPageActive before adding
pages into unevictable list.  It also cleans up VM_BUG_ONs.
Signed-off-by: Naoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Mel Gorman <mgorman@suse.de>
Cc: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Cc: "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/swap.c

@@ -512,12 +512,7 @@ EXPORT_SYMBOL(__lru_cache_add);
  */
 void lru_cache_add(struct page *page)
 {
-	if (PageActive(page)) {
-		VM_BUG_ON(PageUnevictable(page));
-	} else if (PageUnevictable(page)) {
-		VM_BUG_ON(PageActive(page));
-	}
-
+	VM_BUG_ON(PageActive(page) && PageUnevictable(page));
 	VM_BUG_ON(PageLRU(page));
 	__lru_cache_add(page);
 }
@@ -539,6 +534,7 @@ void add_page_to_unevictable_list(struct page *page)
 
 	spin_lock_irq(&zone->lru_lock);
 	lruvec = mem_cgroup_page_lruvec(page, zone);
+	ClearPageActive(page);
 	SetPageUnevictable(page);
 	SetPageLRU(page);
 	add_page_to_lru_list(page, lruvec, LRU_UNEVICTABLE);
@@ -833,7 +829,6 @@ static void __pagevec_lru_add_fn(struct page *page, struct lruvec *lruvec,
 	int active = PageActive(page);
 	enum lru_list lru = page_lru(page);
 
-	VM_BUG_ON(PageUnevictable(page));
 	VM_BUG_ON(PageLRU(page));
 
 	SetPageLRU(page);