[RFC PATCH 3/5] mm: shmem: add THP validation for PMD-mapped THP related statistics

[Baolin Wang]

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

Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
---
 mm/shmem.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/mm/shmem.c b/mm/shmem.c
index 893c88efc45f..b4afda71a3f0 100644
--- a/mm/shmem.c
+++ b/mm/shmem.c
@@ -1662,7 +1662,7 @@ static struct folio *shmem_alloc_and_add_folio(gfp_t gfp,
 			return ERR_PTR(-E2BIG);
 
 		folio = shmem_alloc_hugefolio(gfp, info, index, order);
-		if (!folio)
+		if (!folio && pages == HPAGE_PMD_NR)
 			count_vm_event(THP_FILE_FALLBACK);
 	} else {
 		pages = 1;
@@ -1680,7 +1680,7 @@ 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);
 		}
@@ -2046,7 +2046,8 @@ 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)
-- 
2.39.3