Re: [PATCH v2 2/2] arm64/hugetlb: Implement arm64 specific huge_ptep_get()

[Baolin Wang]

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@xxxxxxxxxx/
>
> Might be worth mentioning that arm64 now enables __HAVE_ARCH_HUGE_PTEP_GET.

Sure.

> > Suggested-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > Signed-off-by: Baolin Wang <baolin.wang@xxxxxxxxxxxxxxxxx>
> > Reviewed-by: Muchun Song <songmuchun@xxxxxxxxxxxxx>
> > ---
> >   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@xxxxxxx>

Thanks for reviewing.