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Subject: Re: [PATCHv2 3/8] khugepaged: Drain all LRU caches before scanning
 pages
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>
 <20200403112928.19742-4-kirill.shutemov@linux.intel.com>
From:   Yang Shi <yang.shi@linux.alibaba.com>
Message-ID: <3f0514c3-7f1e-0ba0-b458-683600bd5905@linux.alibaba.com>
Date:   Mon, 6 Apr 2020 11:15:58 -0700
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On 4/3/20 4:29 AM, Kirill A. Shutemov wrote:
> Having a page in LRU add cache offsets page refcount and gives
> false-negative on PageLRU(). It reduces collapse success rate.
>
> Drain all LRU add caches before scanning. It happens relatively
> rare and should not disturb the system too much.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>

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

> ---
>   mm/khugepaged.c | 2 ++
>   1 file changed, 2 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 14d7afc90786..fdc10ffde1ca 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2065,6 +2065,8 @@ static void khugepaged_do_scan(void)
>   
>   	barrier(); /* write khugepaged_pages_to_scan to local stack */
>   
> +	lru_add_drain_all();
> +
>   	while (progress < pages) {
>   		if (!khugepaged_prealloc_page(&hpage, &wait))
>   			break;