linux-kernel - Re: [PATCH v4 4/5] arm64: mm: implement the architecture-specific clear_flush_young

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Message-ID: <ca465273-13ec-4397-a4f0-a38ad0dab2dc@arm.com>
Date: Wed, 24 Dec 2025 14:09:51 +0000
From: Ryan Roberts <ryan.roberts@....com>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 david@...nel.org, catalin.marinas@....com, will@...nel.org
Cc: lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
 rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, riel@...riel.com,
 harry.yoo@...cle.com, jannh@...gle.com, willy@...radead.org,
 baohua@...nel.org, dev.jain@....com, linux-mm@...ck.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 4/5] arm64: mm: implement the architecture-specific
 clear_flush_young_ptes()

On 23/12/2025 05:48, 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
> 
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>

Reviewed-by: Ryan Roberts <ryan.roberts@....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 d5fbe72e820a..84a6bdabb1f9 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, CONT_PTES);
>  }
>  
> +#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))))
> +		return __ptep_clear_flush_young(vma, addr, ptep);
> +
> +	return contpte_clear_flush_young_ptes(vma, addr, ptep, nr);
> +}
> +
>  #define wrprotect_ptes wrprotect_ptes
>  static __always_inline void wrprotect_ptes(struct mm_struct *mm,
>  				unsigned long addr, pte_t *ptep, unsigned int nr)