Re: [v3 PATCH 5/7] mm: thp: kill transparent_hugepage_active()

["Zach O'Keefe" <zokeefe@google.com>]

On Mon, Jun 6, 2022 at 2:44 PM Yang Shi <shy828301@gmail.com> wrote:
>
> The transparent_hugepage_active() was introduced to show THP eligibility
> bit in smaps in proc, smaps is the only user.  But it actually does the
> similar check as hugepage_vma_check() which is used by khugepaged.  We
> definitely don't have to maintain two similar checks, so kill
> transparent_hugepage_active().

I never realized smaps was the only user! Great!

> Also move hugepage_vma_check() to huge_memory.c and huge_mm.h since it
> is not only for khugepaged anymore.
>
> Signed-off-by: Yang Shi <shy828301@gmail.com>
> ---
>  fs/proc/task_mmu.c         |  2 +-
>  include/linux/huge_mm.h    | 16 +++++++-----
>  include/linux/khugepaged.h |  4 +--
>  mm/huge_memory.c           | 50 ++++++++++++++++++++++++++++++++-----
>  mm/khugepaged.c            | 51 +++-----------------------------------
>  5 files changed, 60 insertions(+), 63 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 2dd8c8a66924..fd79566e204c 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -860,7 +860,7 @@ static int show_smap(struct seq_file *m, void *v)
>         __show_smap(m, &mss, false);
>
>         seq_printf(m, "THPeligible:    %d\n",
> -                  transparent_hugepage_active(vma));
> +                  hugepage_vma_check(vma, vma->vm_flags, true));
>
>         if (arch_pkeys_enabled())
>                 seq_printf(m, "ProtectionKey:  %8u\n", vma_pkey(vma));
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 79d5919beb83..f561c3e16def 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -209,7 +209,9 @@ static inline bool file_thp_enabled(struct vm_area_struct *vma)
>                !inode_is_open_for_write(inode) && S_ISREG(inode->i_mode);
>  }
>
> -bool transparent_hugepage_active(struct vm_area_struct *vma);
> +bool hugepage_vma_check(struct vm_area_struct *vma,
> +                       unsigned long vm_flags,
> +                       bool smaps);
>
>  #define transparent_hugepage_use_zero_page()                           \
>         (transparent_hugepage_flags &                                   \
> @@ -358,11 +360,6 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>         return false;
>  }
>
> -static inline bool transparent_hugepage_active(struct vm_area_struct *vma)
> -{
> -       return false;
> -}
> -
>  static inline bool transhuge_vma_size_ok(struct vm_area_struct *vma)
>  {
>         return false;
> @@ -380,6 +377,13 @@ static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
>         return false;
>  }
>
> +static inline bool hugepage_vma_check(struct vm_area_struct *vma,
> +                                      unsigned long vm_flags,
> +                                      bool smaps)
> +{
> +       return false;
> +}
> +
>  static inline void prep_transhuge_page(struct page *page) {}
>
>  #define transparent_hugepage_flags 0UL
> diff --git a/include/linux/khugepaged.h b/include/linux/khugepaged.h
> index 392d34c3c59a..8a6452e089ca 100644
> --- a/include/linux/khugepaged.h
> +++ b/include/linux/khugepaged.h
> @@ -10,8 +10,6 @@ extern struct attribute_group khugepaged_attr_group;
>  extern int khugepaged_init(void);
>  extern void khugepaged_destroy(void);
>  extern int start_stop_khugepaged(void);
> -extern bool hugepage_vma_check(struct vm_area_struct *vma,
> -                              unsigned long vm_flags);
>  extern void __khugepaged_enter(struct mm_struct *mm);
>  extern void __khugepaged_exit(struct mm_struct *mm);
>  extern void khugepaged_enter_vma(struct vm_area_struct *vma,
> @@ -57,7 +55,7 @@ static inline void khugepaged_enter(struct vm_area_struct *vma,
>  {
>         if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
>             khugepaged_enabled()) {
> -               if (hugepage_vma_check(vma, vm_flags))
> +               if (hugepage_vma_check(vma, vm_flags, false))
>                         __khugepaged_enter(vma->vm_mm);
>         }
>  }
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 36ada544e494..bc8370856e85 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -69,18 +69,56 @@ static atomic_t huge_zero_refcount;
>  struct page *huge_zero_page __read_mostly;
>  unsigned long huge_zero_pfn __read_mostly = ~0UL;
>
> -bool transparent_hugepage_active(struct vm_area_struct *vma)
> +bool hugepage_vma_check(struct vm_area_struct *vma,
> +                       unsigned long vm_flags,
> +                       bool smaps)
>  {
> +       if (!transhuge_vma_enabled(vma, vm_flags))
> +               return false;
> +
> +       if (vm_flags & VM_NO_KHUGEPAGED)
> +               return false;
> +
> +       /* Don't run khugepaged against DAX vma */
> +       if (vma_is_dax(vma))
> +               return false;
> +
> +       if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> +                               vma->vm_pgoff, HPAGE_PMD_NR))
> +               return false;
> +
>         if (!transhuge_vma_size_ok(vma))
>                 return false;
> -       if (vma_is_anonymous(vma))
> -               return __transparent_hugepage_enabled(vma);
> -       if (vma_is_shmem(vma))
> +
> +       /* Enabled via shmem mount options or sysfs settings. */
> +       if (shmem_file(vma->vm_file))
>                 return shmem_huge_enabled(vma);
> -       if (transhuge_vma_enabled(vma, vma->vm_flags) && file_thp_enabled(vma))
> +
> +       if (!khugepaged_enabled())
> +               return false;
> +
> +       /* THP settings require madvise. */
> +       if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> +               return false;
> +
> +       /* Only regular file is valid */
> +       if (file_thp_enabled(vma))
>                 return true;
>
> -       return false;
> +       if (!vma_is_anonymous(vma))
> +               return false;
> +
> +       if (vma_is_temporary_stack(vma))
> +               return false;
> +
> +       /*
> +        * THPeligible bit of smaps should show 1 for proper VMAs even
> +        * though anon_vma is not initialized yet.
> +        */
> +       if (!vma->anon_vma)
> +               return smaps;
> +
> +       return true;
>  }

There are a few cases where the return value for smaps will be
different from before. I presume this won't be an issue, and that any
difference resulting from this change is actually a positive
difference, given it more accurately reflects the thp eligibility of
the vma? For example, a VM_NO_KHUGEPAGED-marked vma might now show 0
where it otherwise showed 1.

>  static bool get_huge_zero_page(void)
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index ca1754d3a827..aa0769e3b0d9 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -437,49 +437,6 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
>         return atomic_read(&mm->mm_users) == 0;
>  }
>
> -bool hugepage_vma_check(struct vm_area_struct *vma,
> -                       unsigned long vm_flags)
> -{
> -       if (!transhuge_vma_enabled(vma, vm_flags))
> -               return false;
> -
> -       if (vm_flags & VM_NO_KHUGEPAGED)
> -               return false;
> -
> -       /* Don't run khugepaged against DAX vma */
> -       if (vma_is_dax(vma))
> -               return false;
> -
> -       if (vma->vm_file && !IS_ALIGNED((vma->vm_start >> PAGE_SHIFT) -
> -                               vma->vm_pgoff, HPAGE_PMD_NR))
> -               return false;
> -
> -       if (!transhuge_vma_size_ok(vma))
> -               return false;
> -
> -       /* Enabled via shmem mount options or sysfs settings. */
> -       if (shmem_file(vma->vm_file))
> -               return shmem_huge_enabled(vma);
> -
> -       if (!khugepaged_enabled())
> -               return false;
> -
> -       /* THP settings require madvise. */
> -       if (!(vm_flags & VM_HUGEPAGE) && !khugepaged_always())
> -               return false;
> -
> -       /* Only regular file is valid */
> -       if (file_thp_enabled(vma))
> -               return true;
> -
> -       if (!vma->anon_vma || !vma_is_anonymous(vma))
> -               return false;
> -       if (vma_is_temporary_stack(vma))
> -               return false;
> -
> -       return true;
> -}
> -
>  void __khugepaged_enter(struct mm_struct *mm)
>  {
>         struct mm_slot *mm_slot;
> @@ -516,7 +473,7 @@ void khugepaged_enter_vma(struct vm_area_struct *vma,
>  {
>         if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
>             khugepaged_enabled()) {
> -               if (hugepage_vma_check(vma, vm_flags))
> +               if (hugepage_vma_check(vma, vm_flags, false))
>                         __khugepaged_enter(vma->vm_mm);
>         }
>  }
> @@ -961,7 +918,7 @@ static int hugepage_vma_revalidate(struct mm_struct *mm, unsigned long address,
>
>         if (!transhuge_vma_suitable(vma, address))
>                 return SCAN_ADDRESS_RANGE;
> -       if (!hugepage_vma_check(vma, vma->vm_flags))
> +       if (!hugepage_vma_check(vma, vma->vm_flags, false))
>                 return SCAN_VMA_CHECK;
>         return 0;
>  }
> @@ -1442,7 +1399,7 @@ void collapse_pte_mapped_thp(struct mm_struct *mm, unsigned long addr)
>          * the valid THP. Add extra VM_HUGEPAGE so hugepage_vma_check()
>          * will not fail the vma for missing VM_HUGEPAGE
>          */
> -       if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE))
> +       if (!hugepage_vma_check(vma, vma->vm_flags | VM_HUGEPAGE, false))
>                 return;
>
>         /* Keep pmd pgtable for uffd-wp; see comment in retract_page_tables() */
> @@ -2132,7 +2089,7 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
>                         progress++;
>                         break;
>                 }
> -               if (!hugepage_vma_check(vma, vma->vm_flags)) {
> +               if (!hugepage_vma_check(vma, vma->vm_flags, false)) {
>  skip:
>                         progress++;
>                         continue;
> --
> 2.26.3
>
>