linux-kernel - Re: [PATCH v6 4/5] arm64: mm: implement the architecture-specific clear_flush_young

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Message-ID: <10f061c9-5c9a-4e8a-8790-a2a68b38ff33@kernel.org>
Date: Mon, 9 Feb 2026 16:30:15 +0100
From: "David Hildenbrand (Arm)" <david@...nel.org>
To: Baolin Wang <baolin.wang@...ux.alibaba.com>, akpm@...ux-foundation.org,
 catalin.marinas@....com, will@...nel.org
Cc: lorenzo.stoakes@...cle.com, ryan.roberts@....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 v6 4/5] arm64: mm: implement the architecture-specific
 clear_flush_young_ptes()

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@....com>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.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@...nel.org>

-- 
Cheers,

David