linux-kernel - Re: [PATCH 4/4] arm64: tlb: set huge page size to stride for hugepage

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Date:   Mon, 31 Jul 2023 16:43:55 +0800
From:   Barry Song <21cnbao@...il.com>
To:     Kefeng Wang <wangkefeng.wang@...wei.com>
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Muchun Song <muchun.song@...ux.dev>,
        Mina Almasry <almasrymina@...gle.com>, kirill@...temov.name,
        joel@...lfernandes.org, william.kucharski@...cle.com,
        kaleshsingh@...gle.com, linux-mm@...ck.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/4] arm64: tlb: set huge page size to stride for hugepage

On Mon, Jul 31, 2023 at 4:33 PM Barry Song <21cnbao@...il.com> wrote:
>
> On Mon, Jul 31, 2023 at 4:14 PM Kefeng Wang <wangkefeng.wang@...wei.com> wrote:
> >
> > It is better to use huge_page_size() for hugepage(HugeTLB) instead of
> > PAGE_SIZE for stride, which has been done in flush_pmd/pud_tlb_range(),
> > it could reduce the loop in __flush_tlb_range().
> >
> > Signed-off-by: Kefeng Wang <wangkefeng.wang@...wei.com>
> > ---
> >  arch/arm64/include/asm/tlbflush.h | 21 +++++++++++----------
> >  1 file changed, 11 insertions(+), 10 deletions(-)
> >
> > diff --git a/arch/arm64/include/asm/tlbflush.h b/arch/arm64/include/asm/tlbflush.h
> > index 412a3b9a3c25..25e35e6f8093 100644
> > --- a/arch/arm64/include/asm/tlbflush.h
> > +++ b/arch/arm64/include/asm/tlbflush.h
> > @@ -360,16 +360,17 @@ static inline void __flush_tlb_range(struct vm_area_struct *vma,
> >         dsb(ish);
> >  }
> >
> > -static inline void flush_tlb_range(struct vm_area_struct *vma,
> > -                                  unsigned long start, unsigned long end)
> > -{
> > -       /*
> > -        * We cannot use leaf-only invalidation here, since we may be invalidating
> > -        * table entries as part of collapsing hugepages or moving page tables.
> > -        * Set the tlb_level to 0 because we can not get enough information here.
> > -        */
> > -       __flush_tlb_range(vma, start, end, PAGE_SIZE, false, 0);
> > -}
> > +/*
> > + * We cannot use leaf-only invalidation here, since we may be invalidating
> > + * table entries as part of collapsing hugepages or moving page tables.
> > + * Set the tlb_level to 0 because we can not get enough information here.
> > + */
> > +#define flush_tlb_range(vma, start, end)                               \
> > +       __flush_tlb_range(vma, start, end,                              \
> > +                               ((vma)->vm_flags & VM_HUGETLB)          \
> > +                               ? huge_page_size(hstate_vma(vma))       \
> > +                               : PAGE_SIZE, false, 0)
> > +
>
> seems like a good idea.
>
> I wonder if a better implementation will be MMU_GATHER_PAGE_SIZE,  in this case,
> we are going to support stride for other large folios as well, such as thp.
>

BTW, in most cases we have already had right stride:

arch/arm64/include/asm/tlb.h has already this to get stride:

static inline void tlb_flush(struct mmu_gather *tlb)
{
   struct vm_area_struct vma = TLB_FLUSH_VMA(tlb->mm, 0);
   bool last_level = !tlb->freed_tables;
   unsigned long stride = tlb_get_unmap_size(tlb);
   int tlb_level = tlb_get_level(tlb);

   /*
    * If we're tearing down the address space then we only care about
    * invalidating the walk-cache, since the ASID allocator won't
    * reallocate our ASID without invalidating the entire TLB.
  */
  if (tlb->fullmm) {
      if (!last_level)
           flush_tlb_mm(tlb->mm);
       return;
  }

   __flush_tlb_range(&vma, tlb->start, tlb->end, stride,
    last_level, tlb_level);
}

> >
> >  static inline void flush_tlb_kernel_range(unsigned long start, unsigned long end)
> >  {
> > --
> > 2.41.0
> >
>
> Thanks
> Barry