[RFC PATCH v2 02/11] mm: khugepaged: generalize collapse_file() for shmem mTHP support

[Baolin Wang]

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

No functional changes in this patch.

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/khugepaged.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/mm/khugepaged.c b/mm/khugepaged.c
index 631459172e19..4adc8c6de062 100644
--- a/mm/khugepaged.c
+++ b/mm/khugepaged.c
@@ -2214,6 +2214,7 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  * @file: file that collapse on
  * @start: collapse start address
  * @cc: collapse context and scratchpad
+ * @order: folio order being collapsed to
  *
  * Basic scheme is simple, details are more complex:
  *  - allocate and lock a new huge page;
@@ -2232,15 +2233,17 @@ static void retract_page_tables(struct address_space *mapping, pgoff_t pgoff)
  *    + unlock and free huge page;
  */
 static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
-		struct file *file, pgoff_t start, struct collapse_control *cc)
+		struct file *file, pgoff_t start, struct collapse_control *cc,
+		int order)
 {
-	const unsigned int max_ptes_none = collapse_max_ptes_none(cc, NULL, HPAGE_PMD_ORDER);
+	const unsigned int max_ptes_none = collapse_max_ptes_none(cc, NULL, order);
 	struct address_space *mapping = file->f_mapping;
+	const unsigned long nr_pages = 1UL << order;
 	struct page *dst;
 	struct folio *folio, *tmp, *new_folio;
-	pgoff_t index = 0, end = start + HPAGE_PMD_NR;
+	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);
 	enum scan_result result = SCAN_SUCCEED;
 	int nr_none = 0;
 	bool is_shmem = shmem_file(file);
@@ -2252,9 +2255,9 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 	 * mapping, the shmem check can be removed.
 	 */
 	VM_WARN_ON_ONCE(!is_shmem && !mapping_pmd_folio_support(mapping));
-	VM_WARN_ON_ONCE(start & (HPAGE_PMD_NR - 1));
+	VM_WARN_ON_ONCE(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;
 
@@ -2591,12 +2594,12 @@ static enum scan_result collapse_file(struct mm_struct *mm, unsigned long addr,
 	}
 
 	if (is_shmem) {
-		lruvec_stat_mod_folio(new_folio, NR_SHMEM, HPAGE_PMD_NR);
+		lruvec_stat_mod_folio(new_folio, NR_SHMEM, nr_pages);
 		lruvec_stat_mod_folio(new_folio, NR_SHMEM_THPS, HPAGE_PMD_NR);
 	} else {
 		lruvec_stat_mod_folio(new_folio, NR_FILE_THPS, HPAGE_PMD_NR);
 	}
-	lruvec_stat_mod_folio(new_folio, NR_FILE_PAGES, HPAGE_PMD_NR);
+	lruvec_stat_mod_folio(new_folio, NR_FILE_PAGES, nr_pages);
 
 	/*
 	 * Mark new_folio as uptodate before inserting it into the
@@ -2604,14 +2607,14 @@ static enum scan_result 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);
@@ -2666,7 +2669,7 @@ static enum scan_result 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;
 }
 
@@ -2769,7 +2772,7 @@ static enum scan_result collapse_scan_file(struct mm_struct *mm,
 			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);
 		}
 	}
 
-- 
2.47.3