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Message-ID: <1beaa7de-4b31-4f19-abee-83872f868e28@arm.com>
Date: Wed, 17 Dec 2025 15:43:41 +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, linux-mm@...ck.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/3] arm64: mm: support batch clearing of the young
flag for large folios
Sorry I'm a bit late to the party...
On 11/12/2025 08:16, Baolin Wang wrote:
> Currently, contpte_ptep_test_and_clear_young() and contpte_ptep_clear_flush_young()
> only clear the young flag and flush TLBs for PTEs within the contiguous range.
> To support batch PTE operations for other sized large folios in the following
> patches, adding a new parameter to specify the number of PTEs.
>
> While we are at it, rename the functions to maintain consistency with other
> contpte_*() functions.
>
> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
> ---
> arch/arm64/include/asm/pgtable.h | 12 ++++-----
> arch/arm64/mm/contpte.c | 44 ++++++++++++++++++++++----------
> 2 files changed, 37 insertions(+), 19 deletions(-)
>
> diff --git a/arch/arm64/include/asm/pgtable.h b/arch/arm64/include/asm/pgtable.h
> index 0944e296dd4a..e03034683156 100644
> --- a/arch/arm64/include/asm/pgtable.h
> +++ b/arch/arm64/include/asm/pgtable.h
> @@ -1679,10 +1679,10 @@ extern void contpte_clear_full_ptes(struct mm_struct *mm, unsigned long addr,
> extern pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
> unsigned long addr, pte_t *ptep,
> unsigned int nr, int full);
> -extern int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep);
> -extern int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep);
> +extern int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep, unsigned int nr);
> +extern int contpte_clear_flush_young_ptes(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep, unsigned int nr);
The "contpte_" functions are intended to be private to the arm64 arch and should
be exposed via the generic APIs. But I don't see any generic batched API for
this, so you're only actually able to pass CONT_PTES as nr. Perhaps you're
planning to define "test_and_clear_young_ptes()" and "clear_flush_young_ptes()"
in later patches?
> extern void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, unsigned int nr);
> extern int contpte_ptep_set_access_flags(struct vm_area_struct *vma,
> @@ -1854,7 +1854,7 @@ static inline int ptep_test_and_clear_young(struct vm_area_struct *vma,
> if (likely(!pte_valid_cont(orig_pte)))
> return __ptep_test_and_clear_young(vma, addr, ptep);
>
> - return contpte_ptep_test_and_clear_young(vma, addr, ptep);
> + return contpte_test_and_clear_young_ptes(vma, addr, ptep, CONT_PTES);
> }
>
> #define __HAVE_ARCH_PTEP_CLEAR_YOUNG_FLUSH
> @@ -1866,7 +1866,7 @@ static inline int ptep_clear_flush_young(struct vm_area_struct *vma,
> if (likely(!pte_valid_cont(orig_pte)))
> return __ptep_clear_flush_young(vma, addr, ptep);
>
> - return contpte_ptep_clear_flush_young(vma, addr, ptep);
> + return contpte_clear_flush_young_ptes(vma, addr, ptep, CONT_PTES);
> }
>
> #define wrprotect_ptes wrprotect_ptes
> diff --git a/arch/arm64/mm/contpte.c b/arch/arm64/mm/contpte.c
> index c0557945939c..19b122441be3 100644
> --- a/arch/arm64/mm/contpte.c
> +++ b/arch/arm64/mm/contpte.c
> @@ -488,8 +488,9 @@ pte_t contpte_get_and_clear_full_ptes(struct mm_struct *mm,
> }
> EXPORT_SYMBOL_GPL(contpte_get_and_clear_full_ptes);
>
> -int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep)
> +int contpte_test_and_clear_young_ptes(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr)
> {
> /*
> * ptep_clear_flush_young() technically requires us to clear the access
> @@ -500,39 +501,56 @@ int contpte_ptep_test_and_clear_young(struct vm_area_struct *vma,
> * having to unfold.
> */
>
> + unsigned long start = addr;
Personally I wouldn't bother defining start - just reuse addr. You're
incrementing start in the below loop, so it's more appropriate to call it addr
anyway.
> + unsigned long end = start + nr * PAGE_SIZE;
> int young = 0;
> int i;
>
> - ptep = contpte_align_down(ptep);
> - addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
> + if (pte_cont(__ptep_get(ptep + nr - 1)))
> + end = ALIGN(end, CONT_PTE_SIZE);
>
> - for (i = 0; i < CONT_PTES; i++, ptep++, addr += PAGE_SIZE)
> - young |= __ptep_test_and_clear_young(vma, addr, ptep);
> + if (pte_cont(__ptep_get(ptep))) {
> + start = ALIGN_DOWN(start, CONT_PTE_SIZE);
> + ptep = contpte_align_down(ptep);
> + }
> +
> + nr = (end - start) / PAGE_SIZE;
> + for (i = 0; i < nr; i++, ptep++, start += PAGE_SIZE)
Given you're now defining end, perhaps we don't need nr?
for (; addr != end; ptep++, addr += PAGE_SIZE)
young |= __ptep_test_and_clear_young(vma, addr, ptep);
> + young |= __ptep_test_and_clear_young(vma, start, ptep);
>
> return young;
> }
> -EXPORT_SYMBOL_GPL(contpte_ptep_test_and_clear_young);
> +EXPORT_SYMBOL_GPL(contpte_test_and_clear_young_ptes);
>
> -int contpte_ptep_clear_flush_young(struct vm_area_struct *vma,
> - unsigned long addr, pte_t *ptep)
> +int contpte_clear_flush_young_ptes(struct vm_area_struct *vma,
> + unsigned long addr, pte_t *ptep,
> + unsigned int nr)
> {
> int young;
>
> - young = contpte_ptep_test_and_clear_young(vma, addr, ptep);
> + young = contpte_test_and_clear_young_ptes(vma, addr, ptep, nr);
>
> if (young) {
> + unsigned long start = addr;
> + unsigned long end = start + nr * PAGE_SIZE;
> +
> + if (pte_cont(__ptep_get(ptep + nr - 1)))
> + end = ALIGN(end, CONT_PTE_SIZE);
> +
> + if (pte_cont(__ptep_get(ptep)))
> + start = ALIGN_DOWN(start, CONT_PTE_SIZE);
> +
We now have this pattern of expanding contpte blocks up and down in 3 places.
Perhaps create a helper?
Thanks,
Ryan
> /*
> * See comment in __ptep_clear_flush_young(); same rationale for
> * eliding the trailing DSB applies here.
> */
> - addr = ALIGN_DOWN(addr, CONT_PTE_SIZE);
> - __flush_tlb_range_nosync(vma->vm_mm, addr, addr + CONT_PTE_SIZE,
> + __flush_tlb_range_nosync(vma->vm_mm, start, end,
> PAGE_SIZE, true, 3);
> }
>
> return young;
> }
> -EXPORT_SYMBOL_GPL(contpte_ptep_clear_flush_young);
> +EXPORT_SYMBOL_GPL(contpte_clear_flush_young_ptes);
>
> void contpte_wrprotect_ptes(struct mm_struct *mm, unsigned long addr,
> pte_t *ptep, unsigned int nr)
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