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

[Kefeng Wang]

On 2023/7/31 16:43, Barry Song wrote:
> On Mon, Jul 31, 2023 at 4:33 PM Barry Song <21cnbao@xxxxxxxxx> wrote:
> > On Mon, Jul 31, 2023 at 4:14 PM Kefeng Wang <wangkefeng.wang@xxxxxxxxxx> 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@xxxxxxxxxx>
> > > ---
> > >   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:

MMU_GATHER_PAGE_SIZE works for tlb_flush, but flush_tlb_range()
directly called without mmu_gather, see above 3 patches is to
use correct flush_[hugetlb/pmd/pud]_tlb_range(also there are
some other places, like get_clear_contig_flush/clear_flush on arm64),
so enable MMU_GATHER_PAGE_SIZE for arm64 is independent thing, right?

> 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