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

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

As a result of commit 13f7f78981e4 ("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 <[email protected]>
Cc: Mel Gorman <[email protected]>
Cc: KOSAKI Motohiro <[email protected]>
Cc: "Kirill A. Shutemov" <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>