Re: [PATCH v2] mm: thp: support "THPeligible" semantics for mTHP with anonymous shmem

[Ryan Roberts <ryan.roberts@arm.com>]

On 02/07/2024 03:34, Bang Li wrote:
> After the commit 7fb1b252afb5 ("mm: shmem: add mTHP support for
> anonymous shmem"), we can configure different policies through
> the multi-size THP sysfs interface for anonymous shmem. But
> currently "THPeligible" indicates only whether the mapping is
> eligible for allocating THP-pages as well as the THP is PMD
> mappable or not for anonymous shmem, we need to support semantics
> for mTHP with anonymous shmem similar to those for mTHP with
> anonymous memory.
> 
> Signed-off-by: Bang Li <libang.li@antgroup.com>
> ---
> Changes since v1 [1]:
>  - Put anonymous shmem mthp related logic into
>    thp_vma_allowable_orders() (per David)
> 
> [1] https://lore.kernel.org/linux-mm/20240628104926.34209-1-libang.li@antgroup.com/
> ---
>  include/linux/huge_mm.h | 11 +++++++++++
>  mm/huge_memory.c        | 13 +++++++++----
>  mm/shmem.c              |  9 +--------
>  3 files changed, 21 insertions(+), 12 deletions(-)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 212cca384d7e..f87136f38aa1 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -267,6 +267,10 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>  	return __thp_vma_allowable_orders(vma, vm_flags, tva_flags, orders);
>  }
>  
> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
> +				struct vm_area_struct *vma, pgoff_t index,
> +				bool global_huge);
> +
>  struct thpsize {
>  	struct kobject kobj;
>  	struct list_head node;
> @@ -460,6 +464,13 @@ static inline unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>  	return 0;
>  }
>  
> +static inline unsigned long shmem_allowable_huge_orders(struct inode *inode,
> +				struct vm_area_struct *vma, pgoff_t index,
> +				bool global_huge)
> +{
> +	return 0;
> +}
> +
>  #define transparent_hugepage_flags 0UL
>  
>  #define thp_get_unmapped_area	NULL
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index c7ce28f6b7f3..ea377bb4af91 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -151,10 +151,15 @@ unsigned long __thp_vma_allowable_orders(struct vm_area_struct *vma,
>  	 * Must be done before hugepage flags check since shmem has its
>  	 * own flags.
>  	 */
> -	if (!in_pf && shmem_file(vma->vm_file))
> -		return shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
> -				     !enforce_sysfs, vma->vm_mm, vm_flags)
> -			? orders : 0;
> +	if (!in_pf && shmem_file(vma->vm_file)) {
> +		bool global_huge = shmem_is_huge(file_inode(vma->vm_file), vma->vm_pgoff,
> +							!enforce_sysfs, vma->vm_mm, vm_flags);
> +
> +		if (!vma_is_anon_shmem(vma))
> +			return global_huge? orders : 0;

nit: missing space before '?'

> +		return shmem_allowable_huge_orders(file_inode(vma->vm_file),
> +							vma, vma->vm_pgoff, global_huge);

What's the rationale for splitting these functions into shmem_is_huge() and
shmem_allowable_huge_orders()? Why not just have a single
shmem_allowable_huge_orders() that tells you the answer?

> +	}
>  
>  	if (!vma_is_anonymous(vma)) {
>  		/*
> diff --git a/mm/shmem.c b/mm/shmem.c
> index d495c0701a83..aa85df9c662a 100644
> --- a/mm/shmem.c
> +++ b/mm/shmem.c
> @@ -1622,7 +1622,7 @@ static gfp_t limit_gfp_mask(gfp_t huge_gfp, gfp_t limit_gfp)
>  }
>  
>  #ifdef CONFIG_TRANSPARENT_HUGEPAGE
> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
> +unsigned long shmem_allowable_huge_orders(struct inode *inode,
>  				struct vm_area_struct *vma, pgoff_t index,
>  				bool global_huge)
>  {
> @@ -1707,13 +1707,6 @@ static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault
>  	return orders;
>  }
>  #else
> -static unsigned long shmem_allowable_huge_orders(struct inode *inode,
> -				struct vm_area_struct *vma, pgoff_t index,
> -				bool global_huge)
> -{
> -	return 0;
> -}
> -
>  static unsigned long shmem_suitable_orders(struct inode *inode, struct vm_fault *vmf,
>  					   struct address_space *mapping, pgoff_t index,
>  					   unsigned long orders)