[PATCH 7/7] mm/thp: remap_page() is only needed on anonymous THP

[Hugh Dickins]

THP splitting's unmap_page() only sets TTU_SPLIT_FREEZE when PageAnon,
and migration entries are only inserted when TTU_MIGRATION (unused here)
or TTU_SPLIT_FREEZE is set: so it's just a waste of time for remap_page()
to search for migration entries to remove when !PageAnon.

Fixes: baa355fd3314 ("thp: file pages support for split_huge_page()")
Signed-off-by: Hugh Dickins <hughd@xxxxxxxxxx>
---
 mm/huge_memory.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 305f709a7aca..e4a83e310452 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2354,6 +2354,7 @@ static void unmap_page(struct page *page)
 
 	VM_BUG_ON_PAGE(!PageHead(page), page);
 
+	/* If TTU_SPLIT_FREEZE is ever extended to file, update remap_page() */
 	if (PageAnon(page))
 		ttu_flags |= TTU_SPLIT_FREEZE;
 
@@ -2368,6 +2369,10 @@ static void unmap_page(struct page *page)
 static void remap_page(struct page *page, unsigned int nr)
 {
 	int i;
+
+	/* If TTU_SPLIT_FREEZE is ever extended to file, remove this check */
+	if (!PageAnon(page))
+		return;
 	if (PageTransHuge(page)) {
 		remove_migration_ptes(page, page, true);
 	} else {
-- 
2.32.0.rc0.204.g9fa02ecfa5-goog