mm: use a folio in fault_dirty_shared_page()

{

	struct vm_area_struct *vma = vmf->vma;

	struct address_space *mapping;

	struct page *page = vmf->page;

	struct folio *folio = page_folio(vmf->page);

	bool dirtied;

	bool page_mkwrite = vma->vm_ops && vma->vm_ops->page_mkwrite;

	dirtied = set_page_dirty(page);

	VM_BUG_ON_PAGE(PageAnon(page), page);

	dirtied = folio_mark_dirty(folio);

	VM_BUG_ON_FOLIO(folio_test_anon(folio), folio);

	/*

	 * Take a local copy of the address_space - page.mapping may be zeroed

	 * by truncate after unlock_page().   The address_space itself remains

	 * pinned by vma->vm_file's reference.  We rely on unlock_page()'s

	 * Take a local copy of the address_space - folio.mapping may be zeroed

	 * by truncate after folio_unlock().   The address_space itself remains

	 * pinned by vma->vm_file's reference.  We rely on folio_unlock()'s

	 * release semantics to prevent the compiler from undoing this copying.

	 */

	mapping = page_rmapping(page);

	unlock_page(page);

	mapping = folio_raw_mapping(folio);

	folio_unlock(folio);

	if (!page_mkwrite)

		file_update_time(vma->vm_file);