rmap: convert page_move_anon_rmap() to use a folio

Removes one call to compound_head() and a reference to page->mapping.

Link: https://lkml.kernel.org/r/20220902194653.1739778-50-willy@infradead.orgSigned-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/rmap.c

@@ -1099,22 +1099,20 @@ int pfn_mkclean_range(unsigned long pfn, unsigned long nr_pages, pgoff_t pgoff,
  */
 void page_move_anon_rmap(struct page *page, struct vm_area_struct *vma)
 {
-	struct anon_vma *anon_vma = vma->anon_vma;
-	struct page *subpage = page;
-
-	page = compound_head(page);
+	void *anon_vma = vma->anon_vma;
+	struct folio *folio = page_folio(page);
 
-	VM_BUG_ON_PAGE(!PageLocked(page), page);
+	VM_BUG_ON_FOLIO(!folio_test_locked(folio), folio);
 	VM_BUG_ON_VMA(!anon_vma, vma);
 
-	anon_vma = (void *) anon_vma + PAGE_MAPPING_ANON;
+	anon_vma += PAGE_MAPPING_ANON;
 	/*
 	 * Ensure that anon_vma and the PAGE_MAPPING_ANON bit are written
 	 * simultaneously, so a concurrent reader (eg folio_referenced()'s
 	 * folio_test_anon()) will not see one without the other.
 	 */
-	WRITE_ONCE(page->mapping, (struct address_space *) anon_vma);
-	SetPageAnonExclusive(subpage);
+	WRITE_ONCE(folio->mapping, anon_vma);
+	SetPageAnonExclusive(page);
 }
 
 /**