[PATCH v6 4/5] arm64: mm: implement the architecture-specific clear_flush_young_ptes()

[Baolin Wang]

On 2/9/26 11:30 PM, David Hildenbrand (Arm) wrote:
> On 2/9/26 15:07, Baolin Wang wrote:
>> Implement the Arm64 architecture-specific clear_flush_young_ptes() to 
>> enable
>> batched checking of young flags and TLB flushing, improving 
>> performance during
>> large folio reclamation.
>>
>> Performance testing:
>> Allocate 10G clean file-backed folios by mmap() in a memory cgroup, 
>> and try to
>> reclaim 8G file-backed folios via the memory.reclaim interface. I can 
>> observe
>> 33% performance improvement on my Arm64 32-core server (and 10%+ 
>> improvement
>> on my X86 machine). Meanwhile, the hotspot folio_check_references() 
>> dropped
>> from approximately 35% to around 5%.
>>
>> W/o patchset:
>> real    0m1.518s
>> user    0m0.000s
>> sys    0m1.518s
>>
>> W/ patchset:
>> real    0m1.018s
>> user    0m0.000s
>> sys    0m1.018s
>>
>> Reviewed-by: Ryan Roberts <ryan.roberts at arm.com>
>> Signed-off-by: Baolin Wang <baolin.wang at linux.alibaba.com>
>> ---
>>   arch/arm64/include/asm/pgtable.h | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/ 
>> asm/pgtable.h
>> index 3dabf5ea17fa..a17eb8a76788 100644
>> --- a/arch/arm64/include/asm/pgtable.h
>> +++ b/arch/arm64/include/asm/pgtable.h
>> @@ -1838,6 +1838,17 @@ static inline int ptep_clear_flush_young(struct 
>> vm_area_struct *vma,
>>       return contpte_clear_flush_young_ptes(vma, addr, ptep, 1);
>>   }
>> +#define clear_flush_young_ptes clear_flush_young_ptes
>> +static inline int clear_flush_young_ptes(struct vm_area_struct *vma,
>> +                     unsigned long addr, pte_t *ptep,
>> +                     unsigned int nr)
>> +{
>> +    if (likely(nr == 1 && !pte_cont(__ptep_get(ptep))))
> I guess similar cases where we should never end up with non-present ptes 
> should be updated accordingly.
> 
> ptep_test_and_clear_young(), for example, should never be called on non- 
> present ptes.

Yes. I already adrressed this in my follow-up patchset.

> Reviewed-by: David Hildenbrand (Arm) <david at kernel.org>

Thanks.