mm: shmem: add THP validation for PMD-mapped THP related statistics

In order to extend support for mTHP, add THP validation for PMD-mapped THP
related statistics to avoid statistical confusion.

Link: https://lkml.kernel.org/r/c4b04cbd51e6951cc2436a87be8eaa4a1516faec.1718090413.git.baolin.wang@linux.alibaba.comSigned-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
Reviewed-by: Barry Song <v-songbaohua@oppo.com>
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: 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

@@ -1647,7 +1647,7 @@ static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
 			return ERR_PTR(-E2BIG);
 
 		folio = shmem_alloc_folio(gfp, HPAGE_PMD_ORDER, info, index);
-		if (!folio)
+		if (!folio && pages == HPAGE_PMD_NR)
 			count_vm_event(THP_FILE_FALLBACK);
 	} else {
 		pages = 1;
@@ -1665,7 +1665,7 @@ static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
 		if (xa_find(&mapping->i_pages, &index,
 				index + pages - 1, XA_PRESENT)) {
 			error = -EEXIST;
-		} else if (huge) {
+		} else if (pages == HPAGE_PMD_NR) {
 			count_vm_event(THP_FILE_FALLBACK);
 			count_vm_event(THP_FILE_FALLBACK_CHARGE);
 		}
@@ -2031,7 +2031,8 @@ static int shmem_get_folio_gfp(struct inode *inode, pgoff_t index,
 		folio = shmem_alloc_and_add_folio(huge_gfp,
 				inode, index, fault_mm, true);
 		if (!IS_ERR(folio)) {
-			count_vm_event(THP_FILE_ALLOC);
+			if (folio_test_pmd_mappable(folio))
+				count_vm_event(THP_FILE_ALLOC);
 			goto alloced;
 		}
 		if (PTR_ERR(folio) == -EEXIST)