[RFC PATCH v2 01/11] mm: khugepaged: add max_ptes_none check in collapse_file()

[Baolin Wang]

Similar to the anonymous folios collapse, we should also check the
'max_ptes_none' when trying to collapse shmem/file folios, which is
also intended as preparation for shmem mTHP collapse in the
following patches.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/khugepaged.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index b12187709f6d..631459172e19 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2234,6 +2234,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
 static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 		struct file *file, pgoff_t start, struct collapse_control *cc)
 {
+	const unsigned int max_ptes_none = collapse_max_ptes_none(cc, NULL, HPAGE_PMD_ORDER);
 	struct address_space *mapping = file->f_mapping;
 	struct page *dst;
 	struct folio *folio, *tmp, *new_folio;
@@ -2299,7 +2300,13 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 						goto xa_locked;
 					}
 				}
-				nr_none++;
+
+				if (++nr_none > max_ptes_none) {
+					result = SCAN_EXCEED_NONE_PTE;
+					count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
+					goto xa_locked;
+				}
+
 				index++;
 				continue;
 			}
-- 
2.47.3