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SubjectRe: [PATCH v2 2/2] arm64/hugetlb: Implement arm64 specific huge_ptep_get()
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在 5/13/2022 7:03 PM, Anshuman Khandual 写道:
>
>
> On 5/13/22 09:07, Baolin Wang wrote:
>> Now we use huge_ptep_get() to get the pte value of a hugetlb page,
>> however it will only return one specific pte value for the CONT-PTE
>> or CONT-PMD size hugetlb on ARM64 system, which can contain seravel
>
> A small nit.
>
> s/seravel/several

Will fix.

>
>> continuous pte or pmd entries with same page table attributes. And it
>> will not take into account the subpages' dirty or young bits of a
>> CONT-PTE/PMD size hugetlb page.
>>
>> So the huge_ptep_get() is inconsistent with huge_ptep_get_and_clear(),
>> which already takes account the dirty or young bits for any subpages
>> in this CONT-PTE/PMD size hugetlb [1]. Meanwhile we can miss dirty or
>> young flags statistics for hugetlb pages with current huge_ptep_get(),
>> such as the gather_hugetlb_stats() function, and CONT-PTE/PMD hugetlb
>> monitoring with DAMON.
>>
>> Thus define an ARM64 specific huge_ptep_get() implementation, that will
>> take into account any subpages' dirty or young bits for CONT-PTE/PMD size
>> hugetlb page, for those functions that want to check the dirty and young
>> flags of a hugetlb page.
>>
>> [1] https://lore.kernel.org/linux-mm/85bd80b4-b4fd-0d3f-a2e5-149559f2f387@oracle.com/
>
> Might be worth mentioning that arm64 now enables __HAVE_ARCH_HUGE_PTEP_GET.

Sure.

>
>>
>> Suggested-by: Muchun Song <songmuchun@bytedance.com>
>> Signed-off-by: Baolin Wang <baolin.wang@linux.alibaba.com>
>> Reviewed-by: Muchun Song <songmuchun@bytedance.com>
>> ---
>> arch/arm64/include/asm/hugetlb.h | 2 ++
>> arch/arm64/mm/hugetlbpage.c | 24 ++++++++++++++++++++++++
>> 2 files changed, 26 insertions(+)
>>
>> diff --git a/arch/arm64/include/asm/hugetlb.h b/arch/arm64/include/asm/hugetlb.h
>> index 616b2ca..1fd2846 100644
>> --- a/arch/arm64/include/asm/hugetlb.h
>> +++ b/arch/arm64/include/asm/hugetlb.h
>> @@ -44,6 +44,8 @@ extern pte_t huge_ptep_clear_flush(struct vm_area_struct *vma,
>> #define __HAVE_ARCH_HUGE_PTE_CLEAR
>> extern void huge_pte_clear(struct mm_struct *mm, unsigned long addr,
>> pte_t *ptep, unsigned long sz);
>> +#define __HAVE_ARCH_HUGE_PTEP_GET
>> +extern pte_t huge_ptep_get(pte_t *ptep);
>> extern void set_huge_swap_pte_at(struct mm_struct *mm, unsigned long addr,
>> pte_t *ptep, pte_t pte, unsigned long sz);
>> #define set_huge_swap_pte_at set_huge_swap_pte_at
>> diff --git a/arch/arm64/mm/hugetlbpage.c b/arch/arm64/mm/hugetlbpage.c
>> index 9553851..9a3f7f1 100644
>> --- a/arch/arm64/mm/hugetlbpage.c
>> +++ b/arch/arm64/mm/hugetlbpage.c
>> @@ -158,6 +158,30 @@ static inline int num_contig_ptes(unsigned long size, size_t *pgsize)
>> return contig_ptes;
>> }
>>
>> +pte_t huge_ptep_get(pte_t *ptep)
>> +{
>> + int ncontig, i;
>> + size_t pgsize;
>> + pte_t orig_pte = ptep_get(ptep);
>> +
>> + if (!pte_present(orig_pte) || !pte_cont(orig_pte))
>> + return orig_pte;
>> +
>> + ncontig = num_contig_ptes(page_size(pte_page(orig_pte)), &pgsize);
>
> Hmm, I guess there is no better way of deriving page size here.
>
> Please drop the extra line here.

OK.

>
>> +
>> + for (i = 0; i < ncontig; i++, ptep++) {
>> + pte_t pte = ptep_get(ptep);
>> +
>> + if (pte_dirty(pte))
>> + orig_pte = pte_mkdirty(orig_pte);
>> +
>> + if (pte_young(pte))
>> + orig_pte = pte_mkyoung(orig_pte);
>> + }
>
> Please drop the extra line here.

Sure.

>
>> +
>> + return orig_pte;
>> +}
>> +
>> /*
>> * Changing some bits of contiguous entries requires us to follow a
>> * Break-Before-Make approach, breaking the whole contiguous set
> Otherwise LGTM.
>
> With those small changes accommodated,
>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@arm.com>

Thanks for reviewing.

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