[PATCH] mm/hugetlb: avoid unnecessary check on pud and pmd entry in huge_pte_offset

[Li Xinhai <lixinhai.lxh@gmail.com>]

When huge_pte_offset() is called, the parameter sz can only be PUD_SIZE
or PMD_SIZE.
If sz is PUD_SIZE and code can reach pud, then *pud must be none, or
normal hugetlb entry, or non-present (migration or hwpoisoned) hugetlb
entry, and we can directly return pud.
When sz is PMD_SIZE, pud must be none or present, and if code can reach
pmd, we can directly return pmd.

So, after this patch, the code is simplified by first check on the
parameter sz, and avoid unnecessary checks in current code.

Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
Cc: Mike Kravetz <mike.kravetz@oracle.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
---
 mm/hugetlb.c | 24 +++++++++---------------
 1 file changed, 9 insertions(+), 15 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index bcabbe0..e1424f5 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -5365,8 +5365,8 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 {
 	pgd_t *pgd;
 	p4d_t *p4d;
-	pud_t *pud, pud_entry;
-	pmd_t *pmd, pmd_entry;
+	pud_t *pud;
+	pmd_t *pmd;
 
 	pgd = pgd_offset(mm, addr);
 	if (!pgd_present(*pgd))
@@ -5376,22 +5376,16 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 		return NULL;
 
 	pud = pud_offset(p4d, addr);
-	pud_entry = READ_ONCE(*pud);
-	if (sz != PUD_SIZE && pud_none(pud_entry))
-		return NULL;
-	/* hugepage or swap? */
-	if (pud_huge(pud_entry) || !pud_present(pud_entry))
+	if (sz == PUD_SIZE)
+		/* must be pud_huge or pud_none */
 		return (pte_t *)pud;
-
-	pmd = pmd_offset(pud, addr);
-	pmd_entry = READ_ONCE(*pmd);
-	if (sz != PMD_SIZE && pmd_none(pmd_entry))
+	if (!pud_present(*pud))
 		return NULL;
-	/* hugepage or swap? */
-	if (pmd_huge(pmd_entry) || !pmd_present(pmd_entry))
-		return (pte_t *)pmd;
+	/* must have a valid entry and size to go further */
 
-	return NULL;
+	pmd = pmd_offset(pud, addr);
+	/* must be pmd_huge or pmd_none */
+	return (pte_t *)pmd;
 }
 
 #endif /* CONFIG_ARCH_WANT_GENERAL_HUGETLB */
-- 
1.8.3.1