rmap: add folio parameter to __page_set_anon_rmap()

Avoid the compound_head() call in PageAnon() by passing in the folio that
all callers have.  Also save me from wondering whether page->mapping can
ever be overwritten on a tail page (I don't think it can, but I'm not 100%
sure).

Link: https://lkml.kernel.org/r/20230116192959.2147032-1-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Reviewed-by: William Kucharski <william.kucharski@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -1131,19 +1131,20 @@ void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
 
 /**
  * __page_set_anon_rmap - set up new anonymous rmap
- * @page:	Page or Hugepage to add to rmap
+ * @folio:	Folio which contains page.
+ * @page:	Page to add to rmap.
  * @vma:	VM area to add page to.
  * @address:	User virtual address of the mapping	
  * @exclusive:	the page is exclusively owned by the current process
  */
-static void __page_set_anon_rmap(struct page *page,
+static void __page_set_anon_rmap(struct folio *folio, struct page *page,
 	struct vm_area_struct *vma, unsigned long address, int exclusive)
 {
 	struct anon_vma *anon_vma = vma->anon_vma;
 
 	BUG_ON(!anon_vma);
 
-	if (PageAnon(page))
+	if (folio_test_anon(folio))
 		goto out;
 
 	/*
@@ -1155,14 +1156,14 @@ static void __page_set_anon_rmap(struct page *page,
 		anon_vma = anon_vma->root;
 
 	/*
-	 * page_idle does a lockless/optimistic rmap scan on page->mapping.
+	 * page_idle does a lockless/optimistic rmap scan on folio->mapping.
 	 * Make sure the compiler doesn't split the stores of anon_vma and
 	 * the PAGE_MAPPING_ANON type identifier, otherwise the rmap code
 	 * could mistake the mapping for a struct address_space and crash.
 	 */
 	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
-	WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
-	page->index = linear_page_index(vma, address);
+	WRITE_ONCE(folio->mapping, (struct address_space *) anon_vma);
+	folio->index = linear_page_index(vma, address);
 out:
 	if (exclusive)
 		SetPageAnonExclusive(page);
@@ -1254,7 +1255,7 @@ void page_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
 	if (likely(!folio_test_ksm(folio))) {
 		/* address might be in next vma when migration races vma_adjust */
 		if (first)
-			__page_set_anon_rmap(page, vma, address,
+			__page_set_anon_rmap(folio, page, vma, address,
 					     !!(flags & RMAP_EXCLUSIVE));
 		else
 			__page_check_anon_rmap(page, vma, address);
@@ -1297,7 +1298,7 @@ void folio_add_new_anon_rmap(struct folio *folio, struct vm_area_struct *vma,
 	}
 
 	__lruvec_stat_mod_folio(folio, NR_ANON_MAPPED, nr);
-	__page_set_anon_rmap(&folio->page, vma, address, 1);
+	__page_set_anon_rmap(folio, &folio->page, vma, address, 1);
 }
 
 /**
@@ -2528,7 +2529,7 @@ void hugepage_add_anon_rmap(struct page *page, struct vm_area_struct *vma,
 	VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page);
 	VM_BUG_ON_PAGE(!first && PageAnonExclusive(page), page);
 	if (first)
-		__page_set_anon_rmap(page, vma, address,
+		__page_set_anon_rmap(folio, page, vma, address,
 				     !!(flags & RMAP_EXCLUSIVE));
 }
 
@@ -2541,6 +2542,6 @@ void hugepage_add_new_anon_rmap(struct page *page,
 	/* increment count (starts at -1) */
 	atomic_set(&folio->_entire_mapcount, 0);
 	folio_clear_hugetlb_restore_reserve(folio);
-	__page_set_anon_rmap(page, vma, address, 1);
+	__page_set_anon_rmap(folio, page, vma, address, 1);
 }
 #endif /* CONFIG_HUGETLB_PAGE */