mm/vmscan: Free non-shmem folios without splitting them

We have to allocate memory in order to split a file-backed folio, so
it's not a good idea to split them in the memory freeing path.  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>

diff --git a/mm/vmscan.c b/mm/vmscan.c
index a57eb747f08d27664ead7b5d40bf21b84d960b7c..d15a9f08caab7a3d8855229544231f026cdc5d0f 100644 (file)
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1739,8 +1739,8 @@ retry:
                                /* 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_folio_to_list(folio, page_list))
                                goto keep_locked;
                }