Re: [PATCH v4 1/2] mm/tlbbatch: Introduce arch_tlbbatch_should_defer()

[Barry Song]

On Wed, Sep 21, 2022 at 8:45 PM Yicong Yang <yangyicong@xxxxxxxxxx> wrote:
>
> From: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
>
> The entire scheme of deferred TLB flush in reclaim path rests on the
> fact that the cost to refill TLB entries is less than flushing out
> individual entries by sending IPI to remote CPUs. But architecture
> can have different ways to evaluate that. Hence apart from checking
> TTU_BATCH_FLUSH in the TTU flags, rest of the decision should be
> architecture specific.
>
> Signed-off-by: Anshuman Khandual <khandual@xxxxxxxxxxxxxxxxxx>
> [https://lore.kernel.org/linuxppc-dev/20171101101735.2318-2-khandual@xxxxxxxxxxxxxxxxxx/]
> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
> [Rebase and fix incorrect return value type]
> Reviewed-by: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
> Reviewed-by: Anshuman Khandual <anshuman.khandual@xxxxxxx>
> ---

Reviewed-by: Barry Song <baohua@xxxxxxxxxx>

>  arch/x86/include/asm/tlbflush.h | 12 ++++++++++++
>  mm/rmap.c                       |  9 +--------
>  2 files changed, 13 insertions(+), 8 deletions(-)
>
> diff --git a/arch/x86/include/asm/tlbflush.h b/arch/x86/include/asm/tlbflush.h
> index cda3118f3b27..8a497d902c16 100644
> --- a/arch/x86/include/asm/tlbflush.h
> +++ b/arch/x86/include/asm/tlbflush.h
> @@ -240,6 +240,18 @@ static inline void flush_tlb_page(struct vm_area_struct *vma, unsigned long a)
>         flush_tlb_mm_range(vma->vm_mm, a, a + PAGE_SIZE, PAGE_SHIFT, false);
>  }
>
> +static inline bool arch_tlbbatch_should_defer(struct mm_struct *mm)
> +{
> +       bool should_defer = false;
> +
> +       /* If remote CPUs need to be flushed then defer batch the flush */
> +       if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
> +               should_defer = true;
> +       put_cpu();
> +
> +       return should_defer;
> +}
> +
>  static inline u64 inc_mm_tlb_gen(struct mm_struct *mm)
>  {
>         /*
> diff --git a/mm/rmap.c b/mm/rmap.c
> index 93d5a6f793d2..cd8cf5cb0b01 100644
> --- a/mm/rmap.c
> +++ b/mm/rmap.c
> @@ -690,17 +690,10 @@ static void set_tlb_ubc_flush_pending(struct mm_struct *mm, bool writable)
>   */
>  static bool should_defer_flush(struct mm_struct *mm, enum ttu_flags flags)
>  {
> -       bool should_defer = false;
> -
>         if (!(flags & TTU_BATCH_FLUSH))
>                 return false;
>
> -       /* If remote CPUs need to be flushed then defer batch the flush */
> -       if (cpumask_any_but(mm_cpumask(mm), get_cpu()) < nr_cpu_ids)
> -               should_defer = true;
> -       put_cpu();
> -
> -       return should_defer;
> +       return arch_tlbbatch_should_defer(mm);
>  }
>
>  /*
> --
> 2.24.0
>