Re: [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@xxxxxxx>
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > ---
> >   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@xxxxxxxxxx>

Thanks.