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

David Hildenbrand (Arm)
2026-02-09T15:30:29Z

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@arm.com>
> Signed-off-by: Baolin Wang <baolin.wang@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.

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

--
Cheers,

David