linux-kernel - Re: [PATCH v2 2/2] mm: khugepaged: check MMF_DISABLE

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Date:   Wed, 7 Apr 2021 14:40:56 -0700
From:   Yang Shi <shy828301@...il.com>
To:     "Xu, Yanfei" <yanfei.xu@...driver.com>
Cc:     Linux MM <linux-mm@...ck.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] mm: khugepaged: check MMF_DISABLE_THP ahead of
 iterating over vmas

On Tue, Apr 6, 2021 at 8:06 PM <yanfei.xu@...driver.com> wrote:
>
> From: Yanfei Xu <yanfei.xu@...driver.com>
>
> We could check MMF_DISABLE_THP ahead of iterating over all of vma.
> Otherwise if some mm_struct contain a large number of vma, there will
> be amounts meaningless cpu cycles cost.

Reviewed-by: Yang Shi <shy828301@...il.com>

>
> Signed-off-by: Yanfei Xu <yanfei.xu@...driver.com>
> ---
>  mm/khugepaged.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index a6012b9259a2..f4ad25a7db55 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2094,6 +2094,8 @@ static unsigned int khugepaged_scan_mm_slot(unsigned int pages,
>          */
>         if (unlikely(!mmap_read_trylock(mm)))
>                 goto breakouterloop_mmap_lock;
> +       if (test_bit(MMF_DISABLE_THP, &mm->flags))
> +               goto breakouterloop;
>         if (likely(!khugepaged_test_exit(mm)))
>                 vma = find_vma(mm, khugepaged_scan.address);
>
> --
> 2.27.0
>