Re: [RFC PATCH v3 2/5] mm, thp: add bpf thp hook to determine thp allocator

[Usama Arif <usamaarif642@gmail.com>]

On 08/06/2025 08:35, Yafang Shao wrote:
> A new hook bpf_thp_allocator() is added to determine if the THP is
> allocated by khugepaged or by the current task.

I would add in the summary why we need this. I am assuming I will find out
when reviewing the next few patches, but would be good to know here.

> 
> Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
> ---
>  include/linux/huge_mm.h | 10 ++++++++++
>  mm/khugepaged.c         |  2 ++
>  2 files changed, 12 insertions(+)
> 
> diff --git a/include/linux/huge_mm.h b/include/linux/huge_mm.h
> index 2f190c90192d..db2eadd3f65b 100644
> --- a/include/linux/huge_mm.h
> +++ b/include/linux/huge_mm.h
> @@ -190,6 +190,14 @@ static inline bool hugepage_global_always(void)
>  			(1<<TRANSPARENT_HUGEPAGE_FLAG);
>  }
>  
> +#define THP_ALLOC_KHUGEPAGED (1 << 1)
> +#define THP_ALLOC_CURRENT (1 << 2)
> +static inline int bpf_thp_allocator(unsigned long vm_flags,
> +				     unsigned long tva_flags)
> +{
> +	return THP_ALLOC_KHUGEPAGED | THP_ALLOC_CURRENT;

You dont use either vm_flags or tva_flags in this function?
I am guessing you wanted to check if these bits are set here?


But you dont seem to be setting these flags anywhere? I am guessing
its in a future patch. If it is, I would move the setting of these bits
here as its confusing to only see the check without knowing where its  

I feel this patch is broken and needs to be rewritten.
> +}
> +
>  static inline int highest_order(unsigned long orders)
>  {
>  	return fls_long(orders) - 1;
> @@ -290,6 +298,8 @@ unsigned long thp_vma_allowable_orders(struct vm_area_struct *vma,
>  	if ((tva_flags & TVA_ENFORCE_SYSFS) && vma_is_anonymous(vma)) {
>  		unsigned long mask = READ_ONCE(huge_anon_orders_always);
>  
> +		if (!(bpf_thp_allocator(vm_flags, tva_flags) & THP_ALLOC_CURRENT))
> +			return 0;

I am assuming that this is the point to check for allocation, but thp_vma_allowable_orders
is not just used for allocation, its used for in other places as well, like hugepage_vma_revalidate
and swap.

>  		if (vm_flags & VM_HUGEPAGE)
>  			mask |= READ_ONCE(huge_anon_orders_madvise);
>  		if (hugepage_global_always() ||
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 79e208999ddb..18f800fe7335 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -472,6 +472,8 @@ void __khugepaged_enter(struct mm_struct *mm)
>  void khugepaged_enter_vma(struct vm_area_struct *vma,
>  			  unsigned long vm_flags)
>  {
> +	if (!(bpf_thp_allocator(vm_flags, 0) & THP_ALLOC_KHUGEPAGED))
> +		return;
>  	if (!test_bit(MMF_VM_HUGEPAGE, &vma->vm_mm->flags) &&
>  	    hugepage_pmd_enabled()) {
>  		if (__thp_vma_allowable_orders(vma, vm_flags, TVA_ENFORCE_SYSFS,