We have to allocate memory in order to split a file-backed page,
so it's not a good idea to split them.  It also doesn't work for XFS
because pages have an extra reference count from page_has_private() and
split_huge_page() expects that reference to have already been removed.
Unfortunately, we still have to split shmem THPs because we can't handle
swapping out an entire THP yet.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 mm/vmscan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 7a2f25b904d9..8b17e46dbf32 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c

@@ -1470,8 +1470,8 @@ static unsigned int shrink_page_list(struct list_head *page_list,
 				/* Adding to swap updated mapping */
 				mapping = page_mapping(page);
 			}
-		} else if (unlikely(PageTransHuge(page))) {
-			/* Split file THP */
+		} else if (PageSwapBacked(page) && PageTransHuge(page)) {
+			/* Split shmem THP */
 			if (split_huge_page_to_list(page, page_list))
 				goto keep_locked;
 		}

-- 
2.30.2