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Subject: Re: [PATCHv2 2/8] khugepaged: Do not stop collapse if less than half
 PTEs are referenced
To:     "Kirill A. Shutemov" <kirill@shutemov.name>,
        akpm@linux-foundation.org, Andrea Arcangeli <aarcange@redhat.com>
Cc:     Zi Yan <ziy@nvidia.com>, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>
References: <20200403112928.19742-1-kirill.shutemov@linux.intel.com>
 <20200403112928.19742-3-kirill.shutemov@linux.intel.com>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <238a9a53-cf9b-7729-46f1-9b2a5e37571a@linux.alibaba.com>
Date:   Mon, 6 Apr 2020 11:13:35 -0700
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On 4/3/20 4:29 AM, 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
> referenced pages, not only swappingin.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
> Fixes: 0db501f7a34c ("mm, thp: convert from optimistic swapin collapsing to conservative")
> Reviewed-by: Zi Yan <ziy@nvidia.com>
> ---
>   mm/khugepaged.c | 3 ++-
>   1 file changed, 2 insertions(+), 1 deletion(-)

Acked-by: Yang Shi <yang.shi@linux.alibaba.com>

>
> 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;