linux-kernel - Re: [PATCH 3/7] khugepaged: Drain LRU add pagevec to get rid of extra pins

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Date:   Fri, 27 Mar 2020 13:34:20 -0400
From:   Zi Yan <ziy@...dia.com>
To:     "Kirill A. Shutemov" <kirill@...temov.name>
CC:     <akpm@...ux-foundation.org>,
        Andrea Arcangeli <aarcange@...hat.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 3/7] khugepaged: Drain LRU add pagevec to get rid of extra
 pins

On 27 Mar 2020, at 13:05, Kirill A. Shutemov wrote:

> __collapse_huge_page_isolate() may fail due to extra pin in the LRU add
> pagevec. It's petty common for swapin case: we swap in pages just to
> fail due to the extra pin.
>
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
>  mm/khugepaged.c | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/mm/khugepaged.c b/mm/khugepaged.c
> index 14d7afc90786..39e0994abeb8 100644
> --- a/mm/khugepaged.c
> +++ b/mm/khugepaged.c
> @@ -585,11 +585,19 @@ static int __collapse_huge_page_isolate(struct vm_area_struct *vma,
>  		 * The page must only be referenced by the scanned process
>  		 * and page swap cache.
>  		 */
> +		if (page_count(page) != 1 + PageSwapCache(page)) {
> +			/*
> +			 * Drain pagevec and retry just in case we can get rid
> +			 * of the extra pin, like in swapin case.
> +			 */
> +			lru_add_drain();
> +		}
>  		if (page_count(page) != 1 + PageSwapCache(page)) {
>  			unlock_page(page);
>  			result = SCAN_PAGE_COUNT;
>  			goto out;
>  		}
> +
>  		if (pte_write(pteval)) {
>  			writable = true;
>  		} else {
> -- 
> 2.26.0

Looks good to me. Is the added empty line intentional?

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

—
Best Regards,
Yan Zi

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