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

[Kefeng Wang <wangkefeng.wang@huawei.com>]

On 2025/10/13 23:58, David Hildenbrand wrote:
> 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?

There is a atomic read, it may be expensive for 512 times atomic read
for change_pte_range().

> 
> 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.
> 

OK, will change it.