[RFC v2 PATCH 08/17] mm: Implement folio_move_anon_rmap_range()

[Ryan Roberts]

Similar to page_move_anon_rmap() except it can batch-move a range of
pages within a folio for increased efficiency. Will be used to enable
reusing multiple pages from a large anonymous folio in one go.

Signed-off-by: Ryan Roberts <ryan.roberts at arm.com>
---
 include/linux/rmap.h |  2 ++
 mm/rmap.c            | 40 ++++++++++++++++++++++++++++++----------
 2 files changed, 32 insertions(+), 10 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index 5c707f53d7b5..8cb0ba48d58f 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -190,6 +190,8 @@ typedef int __bitwise rmap_t;
  * rmap interfaces called when adding or removing pte of page
  */
 void page_move_anon_rmap(struct page *, struct vm_area_struct *);
+void folio_move_anon_rmap_range(struct folio *folio, struct page *page,
+		int nr, struct vm_area_struct *vma);
 void page_add_anon_rmap(struct page *, struct vm_area_struct *,
 		unsigned long address, rmap_t flags);
 void page_add_new_anon_rmap(struct page *, struct vm_area_struct *,
diff --git a/mm/rmap.c b/mm/rmap.c
index 5148a484f915..1cd8fb0b929f 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1103,19 +1103,22 @@ int folio_total_mapcount(struct folio *folio)
 }

 /**
- * page_move_anon_rmap - move a page to our anon_vma
- * @page:	the page to move to our anon_vma
- * @vma:	the vma the page belongs to
+ * folio_move_anon_rmap_range - batch-move a range of pages within a folio to
+ * our anon_vma; a more efficient version of page_move_anon_rmap().
+ * @folio:      folio that owns the range of pages
+ * @page:       the first page to move to our anon_vma
+ * @nr:         number of pages to move to our anon_vma
+ * @vma:        the vma the page belongs to
  *
- * When a page belongs exclusively to one process after a COW event,
- * that page can be moved into the anon_vma that belongs to just that
- * process, so the rmap code will not search the parent or sibling
- * processes.
+ * When a range of pages belongs exclusively to one process after a COW event,
+ * those pages can be moved into the anon_vma that belongs to just that process,
+ * so the rmap code will not search the parent or sibling processes.
  */
-void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
+void folio_move_anon_rmap_range(struct folio *folio, struct page *page,
+					int nr, struct vm_area_struct *vma)
 {
 	void *anon_vma = vma->anon_vma;
-	struct folio *folio = page_folio(page);
+	int i;

 	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_BUG_ON_VMA(!anon_vma, vma);
@@ -1127,7 +1130,24 @@ void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
 	 * folio_test_anon()) will not see one without the other.
 	 */
 	WRITE_ONCE(folio->mapping, anon_vma);
-	SetPageAnonExclusive(page);
+
+	for (i = 0; i < nr; i++)
+		SetPageAnonExclusive(page++);
+}
+
+/**
+ * page_move_anon_rmap - move a page to our anon_vma
+ * @page:	the page to move to our anon_vma
+ * @vma:	the vma the page belongs to
+ *
+ * When a page belongs exclusively to one process after a COW event,
+ * that page can be moved into the anon_vma that belongs to just that
+ * process, so the rmap code will not search the parent or sibling
+ * processes.
+ */
+void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
+{
+	folio_move_anon_rmap_range(page_folio(page), page, 1, vma);
 }

 /**
--
2.25.1