Re: [PATCH v4] mm/mempolicy,hugetlb: Checking hstate for hugetlbfs page in vma_migratable

[Anshuman Khandual <anshuman.khandual@arm.com>]

On 01/16/2020 09:41 AM, Li Xinhai wrote:
> Checking hstate at early phase when isolating page, instead of during
> unmap and move phase, to avoid useless isolation.
> 
> Signed-off-by: Li Xinhai <lixinhai.lxh@gmail.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Mike Kravetz <mike.kravetz@oracle.com>
> ---

Change log from the previous versions ?

>  include/linux/hugetlb.h   | 10 ++++++++++
>  include/linux/mempolicy.h | 29 +----------------------------
>  mm/mempolicy.c            | 28 ++++++++++++++++++++++++++++
>  3 files changed, 39 insertions(+), 28 deletions(-)
> 
> diff --git a/include/linux/hugetlb.h b/include/linux/hugetlb.h
> index 31d4920..c9d871d 100644
> --- a/include/linux/hugetlb.h
> +++ b/include/linux/hugetlb.h
> @@ -598,6 +598,11 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>  	return arch_hugetlb_migration_supported(h);
>  }
>  
> +static inline bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
> +{
> +	return hugepage_migration_supported(hstate_vma(vma));
> +}

Another wrapper around hugepage_migration_supported() is not necessary. 

> +
>  /*
>   * Movability check is different as compared to migration check.
>   * It determines whether or not a huge page should be placed on
> @@ -809,6 +814,11 @@ static inline bool hugepage_migration_supported(struct hstate *h)
>  	return false;
>  }
>  
> +static inline bool vm_hugepage_migration_supported(struct vm_area_struct *vma)
> +{
> +	return false;
> +}
> +
>  static inline bool hugepage_movable_supported(struct hstate *h)
>  {
>  	return false;
> diff --git a/include/linux/mempolicy.h b/include/linux/mempolicy.h
> index 5228c62..8165278 100644
> --- a/include/linux/mempolicy.h
> +++ b/include/linux/mempolicy.h
> @@ -173,34 +173,7 @@ int do_migrate_pages(struct mm_struct *mm, const nodemask_t *from,
>  extern void mpol_to_str(char *buffer, int maxlen, struct mempolicy *pol);
>  
>  /* Check if a vma is migratable */
> -static inline bool vma_migratable(struct vm_area_struct *vma)
> -{
> -	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
> -		return false;
> -
> -	/*
> -	 * DAX device mappings require predictable access latency, so avoid
> -	 * incurring periodic faults.
> -	 */
> -	if (vma_is_dax(vma))
> -		return false;
> -
> -#ifndef CONFIG_ARCH_ENABLE_HUGEPAGE_MIGRATION
> -	if (vma->vm_flags & VM_HUGETLB)
> -		return false;
> -#endif
> -
> -	/*
> -	 * Migration allocates pages in the highest zone. If we cannot
> -	 * do so then migration (at least from node to node) is not
> -	 * possible.
> -	 */
> -	if (vma->vm_file &&
> -		gfp_zone(mapping_gfp_mask(vma->vm_file->f_mapping))
> -								< policy_zone)
> -			return false;
> -	return true;
> -}

Why vma_migratable() is being moved ?

> +extern bool vma_migratable(struct vm_area_struct *vma);
>  
>  extern int mpol_misplaced(struct page *, struct vm_area_struct *, unsigned long);
>  extern void mpol_put_task_policy(struct task_struct *);
> diff --git a/mm/mempolicy.c b/mm/mempolicy.c
> index 067cf7d..8a01fb1 100644
> --- a/mm/mempolicy.c
> +++ b/mm/mempolicy.c
> @@ -1714,6 +1714,34 @@ static int kernel_get_mempolicy(int __user *policy,
>  
>  #endif /* CONFIG_COMPAT */
>  
> +bool vma_migratable(struct vm_area_struct *vma)
> +{
> +	if (vma->vm_flags & (VM_IO | VM_PFNMAP))
> +		return false;
> +
> +	/*
> +	 * DAX device mappings require predictable access latency, so avoid
> +	 * incurring periodic faults.
> +	 */
> +	if (vma_is_dax(vma))
> +		return false;
> +
> +	if (is_vm_hugetlb_page(vma) &&
> +		!vm_hugepage_migration_supported(vma))
> +		return false;

This (use hugepage_migration_supported instead) can be added above without
the code movement.

> +
> +	/*
> +	 * Migration allocates pages in the highest zone. If we cannot
> +	 * do so then migration (at least from node to node) is not
> +	 * possible.
> +	 */
> +	if (vma->vm_file &&
> +		gfp_zone(mapping_gfp_mask(vma->vm_file->f_mapping))
> +			< policy_zone)
> +		return false;
> +	return true;
> +}
> +
>  struct mempolicy *__get_vma_policy(struct vm_area_struct *vma,
>  						unsigned long addr)
>  {
>