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References: <20200327170601.18563-1-kirill.shutemov@linux.intel.com> <20200327170601.18563-3-kirill.shutemov@linux.intel.com>
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From:   Yang Shi <shy828301@gmail.com>
Date:   Fri, 27 Mar 2020 10:46:55 -0700
Message-ID: <CAHbLzkom4C0qBdMouJF4U+C2my6qySyS6oM3v3Pihx68jfmUzQ@mail.gmail.com>
Subject: Re: [PATCH 2/7] khugepaged: Do not stop collapse if less than half
 PTEs are referenced
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Linux MM <linux-mm@kvack.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
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On Fri, Mar 27, 2020 at 10:06 AM Kirill A. Shutemov
<kirill@shutemov.name> wrote:
>
> __collapse_huge_page_swapin() check number of referenced PTE to decide
> if the memory range is hot enough to justify swapin.
>
> The problem is that it stops collapse altogether if there's not enough
> refereced pages, not only swappingin.

s/refereced/referenced

>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative")
> ---
>  mm/khugepaged.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 99bab7e4d05b..14d7afc90786 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -905,7 +905,8 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
>         /* we only decide to swapin, if there is enough young ptes */
>         if (referenced < HPAGE_PMD_NR/2) {
>                 trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
> -               return false;
> +               /* Do not block collapse, only skip swapping in */
> +               return true;
>         }
>         vmf.pte = pte_offset_map(pmd, address);
>         for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
> --
> 2.26.0
>
>