From: Matthew Wilcox (Oracle) <willy@infradead.org>
Date: Wed, 30 Sep 2020 20:15:46 +0000 (-0400)
Subject: mm/vmscan: Free non-shmem folios without splitting them
X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=820c4e2e6f51;p=linux.git

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 a57eb747f08d2..d15a9f08caab7 100644
--- 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;
 		}