linux-kernel - Re: [PATCHv3, RESEND 3/8] khugepaged: Drain all LRU caches before scanning pages

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Date:   Wed, 15 Apr 2020 13:31:58 -0700
From:   Yang Shi <yang.shi@...ux.alibaba.com>
To:     "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        akpm@...ux-foundation.org, Andrea Arcangeli <aarcange@...hat.com>
Cc:     Zi Yan <ziy@...dia.com>, Ralph Campbell <rcampbell@...dia.com>,
        John Hubbard <jhubbard@...dia.com>,
        William Kucharski <william.kucharski@...cle.com>,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCHv3, RESEND 3/8] khugepaged: Drain all LRU caches before
 scanning pages



On 4/13/20 5:52 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@...ux.intel.com>
> ---
>   mm/khugepaged.c | 2 ++
>   1 file changed, 2 insertions(+)

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

>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 5968ec5ddd6b..ee66c140c2d6 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -2059,6 +2059,8 @@ 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;