[RFC PATCH 02/11] mm: khugepaged: generalize collapse_file for mTHP support

[Baolin Wang <baolin.wang@linux.alibaba.com>]

Generalize the order of the collapse_file() function to support future
file/shmem mTHP collapse.

No functional changes in this patch.

Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
---
 mm/khugepaged.c | 20 +++++++++++---------
 1 file changed, 11 insertions(+), 9 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 5d4493b77f3c..e64ed86d28ca 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2064,21 +2064,23 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  */
 static int collapse_file(struct mm_struct *mm, unsigned long addr,
 			 struct file *file, pgoff_t start,
-			 struct collapse_control *cc)
+			 struct collapse_control *cc,
+			 int order)
 {
 	struct address_space *mapping = file->f_mapping;
 	struct page *dst;
 	struct folio *folio, *tmp, *new_folio;
-	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
+	int nr_pages = 1 << order;
+	pgoff_t index = 0, end = start + nr_pages;
 	LIST_HEAD(pagelist);
-	XA_STATE_ORDER(xas, &mapping->i_pages, start, HPAGE_PMD_ORDER);
+	XA_STATE_ORDER(xas, &mapping->i_pages, start, order);
 	int nr_none = 0, result = SCAN_SUCCEED;
 	bool is_shmem = shmem_file(file);
 
 	VM_BUG_ON(!IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS) && !is_shmem);
-	VM_BUG_ON(start & (HPAGE_PMD_NR - 1));
+	VM_BUG_ON(start & (nr_pages - 1));
 
-	result = alloc_charge_folio(&new_folio, mm, cc, HPAGE_PMD_ORDER);
+	result = alloc_charge_folio(&new_folio, mm, cc, order);
 	if (result != SCAN_SUCCEED)
 		goto out;
 
@@ -2426,14 +2428,14 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 	 * unwritten page.
 	 */
 	folio_mark_uptodate(new_folio);
-	folio_ref_add(new_folio, HPAGE_PMD_NR - 1);
+	folio_ref_add(new_folio, nr_pages - 1);
 
 	if (is_shmem)
 		folio_mark_dirty(new_folio);
 	folio_add_lru(new_folio);
 
 	/* Join all the small entries into a single multi-index entry. */
-	xas_set_order(&xas, start, HPAGE_PMD_ORDER);
+	xas_set_order(&xas, start, order);
 	xas_store(&xas, new_folio);
 	WARN_ON_ONCE(xas_error(&xas));
 	xas_unlock_irq(&xas);
@@ -2496,7 +2498,7 @@ static int collapse_file(struct mm_struct *mm, unsigned long addr,
 	folio_put(new_folio);
 out:
 	VM_BUG_ON(!list_empty(&pagelist));
-	trace_mm_khugepaged_collapse_file(mm, new_folio, index, addr, is_shmem, file, HPAGE_PMD_NR, result);
+	trace_mm_khugepaged_collapse_file(mm, new_folio, index, addr, is_shmem, file, nr_pages, result);
 	return result;
 }
 
@@ -2599,7 +2601,7 @@ static int collapse_scan_file(struct mm_struct *mm, unsigned long addr,
 			result = SCAN_EXCEED_NONE_PTE;
 			count_vm_event(THP_SCAN_EXCEED_NONE_PTE);
 		} else {
-			result = collapse_file(mm, addr, file, start, cc);
+			result = collapse_file(mm, addr, file, start, cc, HPAGE_PMD_ORDER);
 		}
 	}
 
-- 
2.43.5