Re: [PATCH v2 3/5] mm/huge_memory.c: add missing read-only THP checking in transparent_hugepage_enabled()

[David Hildenbrand]

On 29.04.21 15:26, Miaohe Lin 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.
>
> Fixes: 99cb0dbd47a1 ("mm,thp: add read-only THP support for (non-shmem) FS")
> Signed-off-by: Miaohe Lin <linmiaohe@xxxxxxxxxx>
> ---
>   include/linux/huge_mm.h | 21 +++++++++++++++++----
>   mm/huge_memory.c        |  6 ++++++
>   mm/khugepaged.c         |  4 +---
>   mm/shmem.c              |  3 +--
>   4 files changed, 25 insertions(+), 9 deletions(-)
>
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 0a526f211fec..f460b74619fc 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -115,6 +115,16 @@ extern struct kobj_attribute shmem_enabled_attr;
>   
>   extern unsigned long transparent_hugepage_flags;
>   
> +static inline bool transhuge_vma_enabled(struct vm_area_struct *vma,
> +					  unsigned long vm_flags)

You're passing the vma already, why do you pass vma->vm_flags 
separately? It's sufficient to pass in the vma only.

> +{
> +	/* 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
> @@ -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;
>   
> @@ -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..e24a96de2e37 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -68,12 +68,18 @@ bool transparent_hugepage_enabled(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;
>   
> +	if (!transhuge_vma_enabled(vma, vma->vm_flags))
> +		return false;
>   	if (!transhuge_vma_suitable(vma, addr))
>   		return false;
>   	if (vma_is_anonymous(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) && vma->vm_file &&
> +	    !inode_is_open_for_write(vma->vm_file->f_inode) &&
> +	    (vma->vm_flags & VM_EXEC))
> +		return true;

Nit: I'm really wondering why we have 3 different functions that sound 
like they are doing the same thing

transparent_hugepage_enabled(vma)
transhuge_vma_enabled()
transhuge_vma_suitable()

Which check belongs where? Does it really have to be that complicated?

>   
>   	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;


--
Thanks,

David / dhildenb