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

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

On 28/06/2024 11:49, 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>
> ---
>  fs/proc/task_mmu.c      | 10 +++++++---
>  include/linux/huge_mm.h | 11 +++++++++++
>  mm/shmem.c              |  9 +--------
>  3 files changed, 19 insertions(+), 11 deletions(-)
> 
> diff --git a/fs/proc/task_mmu.c b/fs/proc/task_mmu.c
> index 93fb2c61b154..09b5db356886 100644
> --- a/fs/proc/task_mmu.c
> +++ b/fs/proc/task_mmu.c
> @@ -870,6 +870,7 @@ static int show_smap(struct seq_file *m, void *v)
>  {
>  	struct vm_area_struct *vma = v;
>  	struct mem_size_stats mss = {};
> +	bool thp_eligible;
>  
>  	smap_gather_stats(vma, &mss, 0);
>  
> @@ -882,9 +883,12 @@ static int show_smap(struct seq_file *m, void *v)
>  
>  	__show_smap(m, &mss, false);
>  
> -	seq_printf(m, "THPeligible:    %8u\n",
> -		   !!thp_vma_allowable_orders(vma, vma->vm_flags,
> -			   TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL));
> +	thp_eligible = !!thp_vma_allowable_orders(vma, vma->vm_flags,
> +						TVA_SMAPS | TVA_ENFORCE_SYSFS, THP_ORDERS_ALL);
> +	if (vma_is_anon_shmem(vma))
> +		thp_eligible = !!shmem_allowable_huge_orders(file_inode(vma->vm_file),
> +							vma, vma->vm_pgoff, thp_eligible);

Afraid I haven't been following the shmem mTHP support work as much as I would
have liked, but is there a reason why we need a separate function for shmem?
Couldn't (shouldn't) thp_vma_allowable_orders() be taught to handle shmem too?

> +	seq_printf(m, "THPeligible:    %8u\n", thp_eligible);
>  
>  	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 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/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)