khugepaged: remove meaningless !pte_present() check in khugepaged_scan_pmd()

We know it must meet the !is_swap_pte() and !pte_none() condition if we
reach here.  Since !is_swap_pte() indicates pte_none() or pte_present()
is met, it's guaranteed that pte must be present here.

Link: https://lkml.kernel.org/r/20210325135647.64106-4-linmiaohe@huawei.comSigned-off-by: Miaohe Lin <linmiaohe@huawei.com>
Reviewed-by: Zi Yan <ziy@nvidia.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

mm/khugepaged.c

@@ -1271,10 +1271,6 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
 				goto out_unmap;
 			}
 		}
-		if (!pte_present(pteval)) {
-			result = SCAN_PTE_NON_PRESENT;
-			goto out_unmap;
-		}
 		if (pte_uffd_wp(pteval)) {
 			/*
 			 * Don't collapse the page if any of the small