mm: use pfn_swap_entry_folio() in copy_nonpresent_pte()

Call pfn_swap_entry_folio() as preparation for converting mm counter
functions to take a folio.

Link: https://lkml.kernel.org/r/20240111152429.3374566-8-willy@infradead.orgSigned-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: David Hildenbrand <david@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/memory.c

@@ -806,9 +806,9 @@ copy_nonpresent_pte(struct mm_struct *dst_mm, struct mm_struct *src_mm,
 		}
 		rss[MM_SWAPENTS]++;
 	} else if (is_migration_entry(entry)) {
-		page = pfn_swap_entry_to_page(entry);
+		folio = pfn_swap_entry_folio(entry);
 
-		rss[mm_counter(page)]++;
+		rss[mm_counter(&folio->page)]++;
 
 		if (!is_readable_migration_entry(entry) &&
 				is_cow_mapping(vm_flags)) {