Re: [PATCH 3/3] mm: huge_memory: use prot_numa_skip() for pmd folio

[David Hildenbrand <david@redhat.com>]

On 13.10.25 14:15, Kefeng Wang wrote:
> The prot_numa_skip() checks should be suitable for pmd folio too,
> which helps to avoid unnecessary pmd change and folio migration
> attempts.
> 
> Signed-off-by: Kefeng Wang <wangkefeng.wang@huawei.com>
> ---
>   mm/huge_memory.c | 21 +++++++--------------
>   mm/internal.h    |  2 ++
>   mm/mprotect.c    |  2 +-
>   3 files changed, 10 insertions(+), 15 deletions(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index 1b81680b4225..feca5a19104a 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2395,8 +2395,7 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   #endif
>   
>   	if (prot_numa) {
> -		struct folio *folio;
> -		bool toptier;
> +		int target_node = NUMA_NO_NODE;
>   		/*
>   		 * Avoid trapping faults against the zero page. The read-only
>   		 * data is likely to be read-cached on the local CPU and
> @@ -2408,19 +2407,13 @@ int change_huge_pmd(struct mmu_gather *tlb, struct vm_area_struct *vma,
>   		if (pmd_protnone(*pmd))
>   			goto unlock;
>   
> -		folio = pmd_folio(*pmd);
> -		toptier = node_is_toptier(folio_nid(folio));
> -		/*
> -		 * Skip scanning top tier node if normal numa
> -		 * balancing is disabled
> -		 */
> -		if (!(sysctl_numa_balancing_mode & NUMA_BALANCING_NORMAL) &&
> -		    toptier)
> -			goto unlock;
> +		/* Get target node for single threaded private VMAs */
> +		if (!(vma->vm_flags & VM_SHARED) &&
> +		    atomic_read(&vma->vm_mm->mm_users) == 1)
> +			target_node = numa_node_id();

Wondering if we should move that hunk into prot_numa_skip() as well.

I'd assume numa_node_id() is not particularly expensive?

While at it, I think we should then rename prot_numa_skip() to
prot_numa_skip_folio() or better "folio_skip_prot_numa()", making folio 
the first parameter.

-- 
Cheers

David / dhildenb