[RFC PATCH 3/5] rmap: add page_add_file_rmap_range()

[Yin Fengwei <fengwei.yin@intel.com>]

page_add_file_rmap_range() allows to add specific range of
large folio rmap.

Signed-off-by: Yin Fengwei <fengwei.yin@intel.com>
---
 include/linux/rmap.h |  2 ++
 mm/rmap.c            | 70 ++++++++++++++++++++++++++++----------------
 2 files changed, 46 insertions(+), 26 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index a6bd1f0a183d..063e0addcbf8 100644
--- a/include/linux/rmap.h
+++ b/include/linux/rmap.h
@@ -198,6 +198,8 @@ void folio_add_new_anon_rmap(struct folio *, struct vm_area_struct *,
 		unsigned long address);
 void page_add_file_rmap(struct page *, struct vm_area_struct *,
 		bool compound);
+void page_add_file_rmap_range(struct folio *, struct page *, int len,
+	struct vm_area_struct *, bool compound);
 void page_remove_rmap(struct page *, struct vm_area_struct *,
 		bool compound);
 
diff --git a/mm/rmap.c b/mm/rmap.c
index 948ca17a96ad..cc7fe3010330 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1301,40 +1301,19 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
 	__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
 }
 
-/**
- * page_add_file_rmap - add pte mapping to a file page
- * @page:	the page to add the mapping to
- * @vma:	the vm area in which the mapping is added
- * @compound:	charge the page as compound or small page
- *
- * The caller needs to hold the pte lock.
- */
-void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
-		bool compound)
+void page_add_file_rmap_range(struct folio *folio, struct page *page, int len,
+	struct vm_area_struct *vma, bool compound)
 {
-	struct folio *folio = page_folio(page);
 	atomic_t *mapped = &folio->_nr_pages_mapped;
-	int nr = 0, nr_pmdmapped = 0;
+	int nr = 0, nr_pmdmapped = 0, nr_pages = folio_nr_pages(folio);
 	bool first;
 
-	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
-
-	/* Is page being mapped by PTE? Is this its first map to be added? */
-	if (likely(!compound)) {
-		first = atomic_inc_and_test(&page->_mapcount);
-		nr = first;
-		if (first && folio_test_large(folio)) {
-			nr = atomic_inc_return_relaxed(mapped);
-			nr = (nr < COMPOUND_MAPPED);
-		}
-	} else if (folio_test_pmd_mappable(folio)) {
-		/* That test is redundant: it's for safety or to optimize out */
-
+	if (compound) {
 		first = atomic_inc_and_test(&folio->_entire_mapcount);
 		if (first) {
 			nr = atomic_add_return_relaxed(COMPOUND_MAPPED, mapped);
 			if (likely(nr < COMPOUND_MAPPED + COMPOUND_MAPPED)) {
-				nr_pmdmapped = folio_nr_pages(folio);
+				nr_pmdmapped = nr_pages;
 				nr = nr_pmdmapped - (nr & FOLIO_PAGES_MAPPED);
 				/* Raced ahead of a remove and another add? */
 				if (unlikely(nr < 0))
@@ -1344,6 +1323,20 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
 				nr = 0;
 			}
 		}
+	} else {
+		int i = 0, new_mapped = 0, count;
+
+		count = min_t(int, len, nr_pages - folio_page_idx(folio, page));
+		do {
+			first = atomic_inc_and_test(&page->_mapcount);
+			new_mapped = first;
+			if (first && folio_test_large(folio)) {
+				new_mapped = atomic_inc_return_relaxed(mapped);
+				new_mapped = (new_mapped < COMPOUND_MAPPED);
+			}
+			if  (new_mapped)
+				nr++;
+		} while (page++, ++i < len);
 	}
 
 	if (nr_pmdmapped)
@@ -1355,6 +1348,31 @@ void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
 	mlock_vma_folio(folio, vma, compound);
 }
 
+/**
+ * page_add_file_rmap - add pte mapping to a file page
+ * @page:	the page to add the mapping to
+ * @vma:	the vm area in which the mapping is added
+ * @compound:	charge the page as compound or small page
+ *
+ * The caller needs to hold the pte lock.
+ */
+void page_add_file_rmap(struct page *page, struct vm_area_struct *vma,
+		bool compound)
+{
+	struct folio *folio = page_folio(page);
+	int nr_pages;
+
+	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
+
+	if (likely(!compound))
+		nr_pages = 1;
+	else
+		nr_pages = folio_nr_pages(folio);
+
+	page_add_file_rmap_range(folio, page, nr_pages, vma, compound);
+}
+
 /**
  * page_remove_rmap - take down pte mapping from a page
  * @page:	page to remove mapping from
-- 
2.30.2