Re: [PATCH 10/16] debug_vm_pgtable/thp: Use page table depost/withdraw with THP

On 8/13/20 10:55 AM, Anshuman Khandual wrote:

On 08/12/2020 12:03 PM, Aneesh Kumar K.V wrote:

quoted

Architectures like ppc64 use deposited page table while updating the huge pte
entries.

Signed-off-by: Aneesh Kumar K.V <redacted>
---
  mm/debug_vm_pgtable.c | 8 ++++++--
  1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index 644d28861ce9..48475d288df1 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c

@@ -147,7 +147,7 @@ static void __init pmd_basic_tests(unsigned long pfn, pgprot_t prot)
  static void __init pmd_advanced_tests(struct mm_struct *mm,
  				      struct vm_area_struct *vma, pmd_t *pmdp,
  				      unsigned long pfn, unsigned long vaddr,
-				      pgprot_t prot)
+				      pgprot_t prot, pgtable_t pgtable)
  {
  	pmd_t pmd;
  

@@ -158,6 +158,8 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
  	/* Align the address wrt HPAGE_PMD_SIZE */
  	vaddr = (vaddr & HPAGE_PMD_MASK) + HPAGE_PMD_SIZE;
  
+	pgtable_trans_huge_deposit(mm, pmdp, pgtable);
+
  	pmd = pmd_mkhuge(pfn_pmd(pfn, prot));
  	set_pmd_at(mm, vaddr, pmdp, pmd);
  	pmdp_set_wrprotect(mm, vaddr, pmdp);

@@ -188,6 +190,8 @@ static void __init pmd_advanced_tests(struct mm_struct *mm,
  	pmdp_test_and_clear_young(vma, vaddr, pmdp);
  	pmd = READ_ONCE(*pmdp);
  	WARN_ON(pmd_young(pmd));
+
+	pgtable = pgtable_trans_huge_withdraw(mm, pmdp);
  }
  
  static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)

@@ -1002,7 +1006,7 @@ static int __init debug_vm_pgtable(void)
  	pgd_clear_tests(mm, pgdp);
  
  	pte_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
-	pmd_advanced_tests(mm, vma, pmdp, pmd_aligned, vaddr, prot);
+	pmd_advanced_tests(mm, vma, pmdp, pmd_aligned, vaddr, prot, saved_ptep);
  	pud_advanced_tests(mm, vma, pudp, pud_aligned, vaddr, prot);
  	hugetlb_advanced_tests(mm, vma, ptep, pte_aligned, vaddr, prot);
  

Makes sense, if it is required for THP to work correctly but needs to be tested
across enabled platforms. Why should not the same apply for pud_advanced_tests()
on platforms that supports PUD based THP.

pud doesn't have page table deposit/withdraw semantics. We use that to 
support hugepage split. With pud mapping we don't split, we just drop 
the hugepage and expect it to be faulted back in as regular page.

-aneesh