mm: shmem: extend shmem_partial_swap_usage() to support large folio swap

To support shmem large folio swapout in the following patches, using
xa_get_order() to get the order of the swap entry to calculate the swap
usage of shmem.

Link: https://lkml.kernel.org/r/60b130b9fc3e422bb91293a172c2113c85e9233a.1723434324.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Cc: Barry Song <baohua@kernel.org>
Cc: Chris Li <chrisl@kernel.org>
Cc: Daniel Gomez <da.gomez@samsung.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: "Huang, Ying" <ying.huang@intel.com>
Cc: Hugh Dickins <hughd@google.com>
Cc: Kefeng Wang <wangkefeng.wang@huawei.com>
Cc: Lance Yang <ioworker0@gmail.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Pankaj Raghav <p.raghav@samsung.com>
Cc: Ryan Roberts <ryan.roberts@arm.com>
Cc: Yang Shi <shy828301@gmail.com>
Cc: Zi Yan <ziy@nvidia.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/shmem.c

@@ -890,7 +890,7 @@ unsigned long shmem_partial_swap_usage(struct address_space *mapping,
 		if (xas_retry(&xas, page))
 			continue;
 		if (xa_is_value(page))
-			swapped++;
+			swapped += 1 << xa_get_order(xas.xa, xas.xa_index);
 		if (xas.xa_index == max)
 			break;
 		if (need_resched()) {