Re: [PATCH v3 3/5] mm/huge_memory.c: add missing read-only THP checking in transparent_hugepage_enabled()

[Yang Shi <shy828301@gmail.com>]

On Tue, May 11, 2021 at 6:49 AM Miaohe Lin <linmiaohe@huawei.com> wrote:
>
> Since commit 99cb0dbd47a1 ("mm,thp: add read-only THP support for
> (non-shmem) FS"), read-only THP file mapping is supported. But it
> forgot to add checking for it in transparent_hugepage_enabled().
> To fix it, we add checking for read-only THP file mapping and also
> introduce helper transhuge_vma_enabled() to check whether thp is
> enabled for specified vma to reduce duplicated code. We rename
> transparent_hugepage_enabled to transparent_hugepage_active to make
> the code easier to follow as suggested by David Hildenbrand.
>
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>

Looks correct to me. Reviewed-by: Yang Shi <shy828301@gmail.com>

Just a nit below:

> ---
>  fs/proc/task_mmu.c      |  2 +-
>  include/linux/huge_mm.h | 27 ++++++++++++++++++++-------
>  mm/huge_memory.c        | 11 ++++++++++-
>  mm/khugepaged.c         |  4 +---
>  mm/shmem.c              |  3 +--
>  5 files changed, 33 insertions(+), 14 deletions(-)
>
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index fc9784544b24..7389df326edd 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -832,7 +832,7 @@ static int show_smap(struct seq_file *m, void *v)
>         __show_smap(m, &mss, false);
>
>         seq_printf(m, "THPeligible:    %d\n",
> -                  transparent_hugepage_enabled(vma));
> +                  transparent_hugepage_active(vma));
>
>         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 0a526f211fec..a35c13d1f487 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -115,9 +115,19 @@ extern struct kobj_attribute shmem_enabled_attr;
>
>  extern unsigned long transparent_hugepage_flags;
>
> +static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,

I'd like to have this function defined next to transhuge_vma_suitable().

> +                                         unsigned long vm_flags)
> +{
> +       /* Explicitly disabled through madvise. */
> +       if ((vm_flags & VM_NOHUGEPAGE) ||
> +           test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> +               return false;
> +       return true;
> +}
> +
>  /*
>   * to be used on vmas which are known to support THP.
> - * Use transparent_hugepage_enabled otherwise
> + * Use transparent_hugepage_active otherwise
>   */
>  static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>  {
> @@ -128,15 +138,12 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>         if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_NEVER_DAX))
>                 return false;
>
> -       if (vma->vm_flags & VM_NOHUGEPAGE)
> +       if (!transhuge_vma_enabled(vma, vma->vm_flags))
>                 return false;
>
>         if (vma_is_temporary_stack(vma))
>                 return false;
>
> -       if (test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> -               return false;
> -
>         if (transparent_hugepage_flags & (1 << TRANSPARENT_HUGEPAGE_FLAG))
>                 return true;
>
> @@ -150,7 +157,7 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>         return false;
>  }
>
> -bool transparent_hugepage_enabled(struct vm_area_struct *vma);
> +bool transparent_hugepage_active(struct vm_area_struct *vma);
>
>  static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>                 unsigned long haddr)
> @@ -351,7 +358,7 @@ static inline bool __transparent_hugepage_enabled(struct vm_area_struct *vma)
>         return false;
>  }
>
> -static inline bool transparent_hugepage_enabled(struct vm_area_struct *vma)
> +static inline bool transparent_hugepage_active(struct vm_area_struct *vma)
>  {
>         return false;
>  }
> @@ -362,6 +369,12 @@ static inline bool transhuge_vma_suitable(struct vm_area_struct *vma,
>         return false;
>  }
>
> +static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
> +                                         unsigned long vm_flags)
> +{
> +       return false;
> +}
> +
>  static inline void prep_transhuge_page(struct page *page) {}
>
>  static inline bool is_transparent_hugepage(struct page *page)
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 76ca1eb2a223..4f37867eed12 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -63,7 +63,14 @@ static struct shrinker deferred_split_shrinker;
>  static atomic_t huge_zero_refcount;
>  struct page *huge_zero_page __read_mostly;
>
> -bool transparent_hugepage_enabled(struct vm_area_struct *vma)
> +static inline bool file_thp_enabled(struct vm_area_struct *vma)
> +{
> +       return transhuge_vma_enabled(vma, vma->vm_flags) && vma->vm_file &&
> +              !inode_is_open_for_write(vma->vm_file->f_inode) &&
> +              (vma->vm_flags & VM_EXEC);
> +}
> +
> +bool transparent_hugepage_active(struct vm_area_struct *vma)
>  {
>         /* The addr is used to check if the vma size fits */
>         unsigned long addr = (vma->vm_end & HPAGE_PMD_MASK) - HPAGE_PMD_SIZE;
> @@ -74,6 +81,8 @@ bool transparent_hugepage_enabled(struct vm_area_struct *vma)
>                 return __transparent_hugepage_enabled(vma);
>         if (vma_is_shmem(vma))
>                 return shmem_huge_enabled(vma);
> +       if (IS_ENABLED(CONFIG_READ_ONLY_THP_FOR_FS))
> +               return file_thp_enabled(vma);
>
>         return false;
>  }
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 6c0185fdd815..d97b20fad6e8 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -442,9 +442,7 @@ static inline int khugepaged_test_exit(struct mm_struct *mm)
>  static bool hugepage_vma_check(struct vm_area_struct *vma,
>                                unsigned long vm_flags)
>  {
> -       /* Explicitly disabled through madvise. */
> -       if ((vm_flags & VM_NOHUGEPAGE) ||
> -           test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> +       if (!transhuge_vma_enabled(vma, vm_flags))
>                 return false;
>
>         /* Enabled via shmem mount options or sysfs settings. */
> diff --git a/mm/shmem.c b/mm/shmem.c
> index a08cedefbfaa..1dcbec313c70 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -4032,8 +4032,7 @@ bool shmem_huge_enabled(struct vm_area_struct *vma)
>         loff_t i_size;
>         pgoff_t off;
>
> -       if ((vma->vm_flags & VM_NOHUGEPAGE) ||
> -           test_bit(MMF_DISABLE_THP, &vma->vm_mm->flags))
> +       if (!transhuge_vma_enabled(vma, vma->vm_flags))
>                 return false;
>         if (shmem_huge == SHMEM_HUGE_FORCE)
>                 return true;
> --
> 2.23.0
>
>