[RFC PATCH v2 3/5] rmap: add page_add_file_rmap_range()

[Yin Fengwei <fengwei.yin@xxxxxxxxx>]

page_add_file_rmap_range() allows to add pte mapping to a specific
range of file folio. Comparing to original page_add_file_rmap(),
it batched updates __lruvec_stat for large folio.

Signed-off-by: Yin Fengwei <fengwei.yin@xxxxxxxxx>
---
 include/linux/rmap.h |  2 ++
 mm/rmap.c            | 66 ++++++++++++++++++++++++++++++++++----------
 2 files changed, 54 insertions(+), 14 deletions(-)

diff --git a/include/linux/rmap.h b/include/linux/rmap.h
index a4570da03e58..9631a3701504 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 *, unsigned long start,
+		unsigned int nr_pages, 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 15ae24585fc4..090de52e1a9a 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1303,31 +1303,44 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
 }
 
 /**
- * page_add_file_rmap - add pte mapping to a file page
- * @page:	the page to add the mapping to
+ * page_add_file_rmap_range - add pte mapping to a sub page range of a folio
+ * @folio:	The filio to add the mapping to
+ * @start:	The first sub page index in folio
+ * @nr_pages:	The number of sub pages from the first page
  * @vma:	the vm area in which the mapping is added
  * @compound:	charge the page as compound or small page
  *
+ * The sub page range of folio is defined by
+ * 	[first_sub_page, first_sub_page + nr_pages)
+ *
  * 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, unsigned long start,
+			unsigned int nr_pages, 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;
-	bool first;
+	unsigned int nr = 0, nr_pmdmapped = 0, first;
 
-	VM_BUG_ON_PAGE(compound && !PageTransHuge(page), page);
+	VM_WARN_ON_FOLIO(compound && !folio_test_pmd_mappable(folio), folio);
 
 	/* 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);
-		}
+		struct page *page = folio_page(folio, start);
+
+		nr_pages = min_t(unsigned int, nr_pages,
+					folio_nr_pages(folio) - start);
+
+		do {
+			first = atomic_inc_and_test(&page->_mapcount);
+			if (first && folio_test_large(folio)) {
+				first = atomic_inc_return_relaxed(mapped);
+				first = (nr < COMPOUND_MAPPED);
+			}
+
+			if (first)
+				nr++;
+		} while (page++, --nr_pages > 0);
 	} else if (folio_test_pmd_mappable(folio)) {
 		/* That test is redundant: it's for safety or to optimize out */
 
@@ -1356,6 +1369,31 @@ 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);
+	unsigned int nr_pages;
+
+	VM_WARN_ON_ONCE_PAGE(compound && !PageTransHuge(page), page);
+
+	if (likely(!compound))
+		nr_pages = 1;
+	else
+		nr_pages = folio_nr_pages(folio);
+
+	page_add_file_rmap_range(folio, folio_page_idx(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