Re: [PATCH v3 08/13] mm/debug_vm_pgtable/thp: Use page table depost/withdraw with THP

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On 9/1/20 8:52 AM, Anshuman Khandual wrote:


On 08/27/2020 01:34 PM, Aneesh Kumar K.V wrote:
Architectures like ppc64 use deposited page table while updating the huge pte
entries.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx>
---
  mm/debug_vm_pgtable.c | 10 +++++++---
  1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/mm/debug_vm_pgtable.c b/mm/debug_vm_pgtable.c
index f9f6358899a8..0ce5c6a24c5b 100644
--- a/mm/debug_vm_pgtable.c
+++ b/mm/debug_vm_pgtable.c
@@ -154,7 +154,7 @@ 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;
@@ -165,6 +165,8 @@ 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);
@@ -193,6 +195,8 @@ 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);

Should the call sites here be wrapped with __HAVE_ARCH_PGTABLE_DEPOSIT and
__HAVE_ARCH_PGTABLE_WITHDRAW respectively. Though there are generic fallback
definitions, wondering whether they are indeed essential for all platforms.


No, because Any page table helpers operating on pmd level THP can expect a deposited page table.

__HAVE_ARCH_PGTABLE_DEPOSIT indicates that fallback to generic version.

  }
static void __init pmd_leaf_tests(unsigned long pfn, pgprot_t prot)
@@ -373,7 +377,7 @@ static void __init pud_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)
  {
  }
  static void __init pud_advanced_tests(struct mm_struct *mm,
@@ -1015,7 +1019,7 @@ 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);

There is a checkpatch.pl warning here.

WARNING: Possible unwrapped commit description (prefer a maximum 75 chars per line)
#7:
Architectures like ppc64 use deposited page table while updating the huge pte

total: 0 errors, 1 warnings, 40 lines checked


I will ignore all these, because they are not really important IMHO.

-aneesh



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