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Message-ID: <96c0adcc-abfd-4a44-be93-1c6bd7942d6d@linux.alibaba.com>
Date: Thu, 18 Dec 2025 15:15:16 +0800
From: Baolin Wang <baolin.wang@...ux.alibaba.com>
To: Ryan Roberts <ryan.roberts@....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
On 2025/12/17 23:43, Ryan Roberts wrote:
> Sorry I'm a bit late to the party...
Never mind. It's not late and comments are always welcome :)
> 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?
Right. This is a preparation patch, and will be used in patch 2.
>> 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.
OK.
>> + 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);
Yes, good point.
>> + 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?
Sounds reasonable. How about the following helper?
static pte_t *contpte_align_addr_ptep(unsigned long *start, unsigned
long *end,
pte_t *ptep, unsigned int nr)
{
unsigned long end_addr = *start + nr * PAGE_SIZE;
if (pte_cont(__ptep_get(ptep + nr - 1)))
*end = ALIGN(end_addr, CONT_PTE_SIZE);
if (pte_cont(__ptep_get(ptep))) {
*start = ALIGN_DOWN(*start, CONT_PTE_SIZE);
ptep = contpte_align_down(ptep);
}
return ptep;
}
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