mm/shmem, swap: fix major fault counting

If the swapin failed, don't update the major fault count.  There is a long
existing comment for doing it this way, now with previous cleanups, we can
finally fix it.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Kairui Song <[email protected]>
Reviewed-by: Baolin Wang <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Barry Song <[email protected]>
Cc: Chris Li <[email protected]>
Cc: Dev Jain <[email protected]>
Cc: Hugh Dickins <[email protected]>
Cc: Kemeng Shi <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Nhat Pham <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: ryncsn

mm/shmem.c

@@ -2356,13 +2356,6 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 	/* Look it up and read it in.. */
 	folio = swap_cache_get_folio(swap, NULL, 0);
 	if (!folio) {
-		/* Or update major stats only when swapin succeeds?? */
-		if (fault_type) {
-			*fault_type |= VM_FAULT_MAJOR;
-			count_vm_event(PGMAJFAULT);
-			count_memcg_event_mm(fault_mm, PGMAJFAULT);
-		}
-
 		if (data_race(si->flags & SWP_SYNCHRONOUS_IO)) {
 			/* Direct swapin skipping swap cache & readahead */
 			folio = shmem_swap_alloc_folio(inode, vma, index,
@@ -2381,6 +2374,11 @@ static int shmem_swapin_folio(struct inode *inode, pgoff_t index,
 				goto failed;
 			}
 		}
+		if (fault_type) {
+			*fault_type |= VM_FAULT_MAJOR;
+			count_vm_event(PGMAJFAULT);
+			count_memcg_event_mm(fault_mm, PGMAJFAULT);
+		}
 	}
 
 	if (order > folio_order(folio)) {