mm: use a folio in fault_dirty_shared_page()

We can replace four implicit calls to compound_head() with one by using
folio.

Link: https://lkml.kernel.org/r/20230701032853.258697-2-zhangpeng362@huawei.comSigned-off-by: ZhangPeng <zhangpeng362@huawei.com>
Reviewed-by: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Reviewed-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Nanyong Sun <sunnanyong@huawei.com>
Cc: Sidhartha Kumar <sidhartha.kumar@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -2965,20 +2965,20 @@ static vm_fault_t fault_dirty_shared_page(struct vm_fault *vmf)
 {
 	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);