linux-kernel - Re: [PATCH v2 2/2] arm64/hugetlb: Implement arm64 specific huge_ptep

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Message-ID: <b7b5fa19-1611-f357-e313-5ea4b82218a2@linux.alibaba.com>
Date:   Sat, 14 May 2022 09:43:03 +0800
From:   Baolin Wang <baolin.wang@...ux.alibaba.com>
To:     Anshuman Khandual <anshuman.khandual@....com>,
        catalin.marinas@....com, will@...nel.org
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        songmuchun@...edance.com, willy@...radead.org,
        christophe.leroy@...roup.eu, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCH v2 2/2] arm64/hugetlb: Implement arm64 specific
 huge_ptep_get()



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@...edance.com>
>> Signed-off-by: Baolin Wang <baolin.wang@...ux.alibaba.com>
>> Reviewed-by: Muchun Song <songmuchun@...edance.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@....com>

Thanks for reviewing.