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From:   Zi Yan <ziy@nvidia.com>
To:     "Kirill A. Shutemov" <kirill@shutemov.name>
CC:     <akpm@linux-foundation.org>,
        Andrea Arcangeli <aarcange@redhat.com>, <linux-mm@kvack.org>,
        <linux-kernel@vger.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
Subject: Re: [PATCH 2/7] khugepaged: Do not stop collapse if less than half
 PTEs are referenced
Date:   Fri, 27 Mar 2020 13:30:26 -0400
Message-ID: <82E3CA05-2AE5-4FB4-860E-F334A99E69FD@nvidia.com>
In-Reply-To: <20200327170601.18563-3-kirill.shutemov@linux.intel.com>
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 <20200327170601.18563-3-kirill.shutemov@linux.intel.com>
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On 27 Mar 2020, at 13:05, Kirill A. Shutemov 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.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsin=
g 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_s=
truct *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 =3D pte_offset_map(pmd, address);
>  	for (; vmf.address < address + HPAGE_PMD_NR*PAGE_SIZE;
> -- =

> 2.26.0

Make sense.

Reviewed-by: Zi Yan <ziy@nvidia.com>

=E2=80=94
Best Regards,
Yan Zi

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