linux-kernel - [RFC PATCH 2/2] mm/hugetlb: Support swap entries in huge_pte

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Date:   Mon, 24 Jul 2017 18:33:18 +0100
From:   Punit Agrawal <punit.agrawal@....com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Punit Agrawal <punit.agrawal@....com>,
        Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org,
        linux-arch@...r.kernel.org, steve.capper@....com,
        will.deacon@....com, catalin.marinas@....com,
        kirill.shutemov@...ux.intel.com, Michal Hocko <mhocko@...e.com>,
        Mike Kravetz <mike.kravetz@...cle.com>
Subject: [RFC PATCH 2/2] mm/hugetlb: Support swap entries in huge_pte_offset()

Although huge_pte_offset() returns NULL when encountering swap page
table entries, the callers of huge_pte_offset() correctly handling swap
entries.

Add support to the huge_pte_offset() to return the swap entries when it
encounters them during the page table walks.

Also update the function documentation to explicitly state this
behaviour. This is to help clarify expectations for architecture
specific implementations of huge_pte_offset().

Signed-off-by: Punit Agrawal <punit.agrawal@....com>
---
 mm/hugetlb.c | 14 ++++++++------
 1 file changed, 8 insertions(+), 6 deletions(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 686eb6fa9eb1..72dd1139a8e4 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -4607,8 +4607,8 @@ pte_t *huge_pte_alloc(struct mm_struct *mm,
  * huge_pte_offset() - Walk the page table to resolve the hugepage
  * entry at address @addr
  *
- * Return: Pointer to page table entry (PUD or PMD) for address @addr
- * or NULL if the entry is not present.
+ * Return: Pointer to page table or swap entry (PUD or PMD) for address @addr
+ * or NULL if the entry is p*d_none().
  */
 pte_t *huge_pte_offset(struct mm_struct *mm,
 		       unsigned long addr, unsigned long sz)
@@ -4626,15 +4626,17 @@ pte_t *huge_pte_offset(struct mm_struct *mm,
 		return NULL;
 
 	pud = pud_offset(p4d, addr);
-	if (!pud_present(*pud))
+	if (pud_none(*pud))
 		return NULL;
-	if (pud_huge(*pud))
+	/* hugepage or swap? */
+	if (pud_huge(*pud) || !pud_present(*pud))
 		return (pte_t *)pud;
 
 	pmd = pmd_offset(pud, addr);
-	if (!pmd_present(*pmd))
+	if (pmd_none(*pmd))
 		return NULL;
-	if (pmd_huge(*pmd))
+	/* hugepage or swap? */
+	if (pmd_huge(*pmd) || !pmd_present(*pmd))
 		return (pte_t *) pmd;
 
 	return NULL;
-- 
2.11.0