linux-kernel - [PATCH 04/12] mm/vmscan: Free non-shmem folios without splitting them

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Message-Id: <20220116121822.1727633-5-willy@infradead.org>
Date:   Sun, 16 Jan 2022 12:18:14 +0000
From:   "Matthew Wilcox (Oracle)" <willy@...radead.org>
To:     linux-kernel@...r.kernel.org, linux-mm@...ck.org,
        linux-fsdevel@...r.kernel.org
Cc:     "Matthew Wilcox (Oracle)" <willy@...radead.org>
Subject: [PATCH 04/12] 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@...radead.org>
---
 mm/vmscan.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/mm/vmscan.c b/mm/vmscan.c
index 700434db5735..45665874082d 100644
--- a/mm/vmscan.c
+++ b/mm/vmscan.c
@@ -1728,8 +1728,8 @@ 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;
 		}
-- 
2.34.1