linux-kernel - Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page to workaround the nasty free_huge

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Message-ID: <20200810021737.GV14854@MiWiFi-R3L-srv>
Date:   Mon, 10 Aug 2020 10:17:37 +0800
From:   Baoquan He <bhe@...hat.com>
To:     Wei Yang <richard.weiyang@...ux.alibaba.com>, mhocko@...nel.org
Cc:     mike.kravetz@...cle.com, akpm@...ux-foundation.org,
        linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 10/10] mm/hugetlb: not necessary to abuse temporary page
 to workaround the nasty free_huge_page

On 08/07/20 at 05:12pm, Wei Yang wrote:
> Let's always increase surplus_huge_pages and so that free_huge_page
> could decrease it at free time.
> 
> Signed-off-by: Wei Yang <richard.weiyang@...ux.alibaba.com>
> ---
>  mm/hugetlb.c | 14 ++++++--------
>  1 file changed, 6 insertions(+), 8 deletions(-)
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index 1f2010c9dd8d..a0eb81e0e4c5 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -1913,21 +1913,19 @@ static struct page *alloc_surplus_huge_page(struct hstate *h, gfp_t gfp_mask,
>  		return NULL;
>  
>  	spin_lock(&hugetlb_lock);
> +
> +	h->surplus_huge_pages++;
> +	h->surplus_huge_pages_node[page_to_nid(page)]++;
> +
>  	/*
>  	 * We could have raced with the pool size change.
>  	 * Double check that and simply deallocate the new page
> -	 * if we would end up overcommiting the surpluses. Abuse
> -	 * temporary page to workaround the nasty free_huge_page
> -	 * codeflow
> +	 * if we would end up overcommiting the surpluses.
>  	 */
> -	if (h->surplus_huge_pages >= h->nr_overcommit_huge_pages) {
> -		SetPageHugeTemporary(page);

Hmm, the temporary page way is taken intentionally in
commit 9980d744a0428 ("mm, hugetlb: get rid of surplus page accounting tricks").
>From code, this is done inside hugetlb_lock holding, and the code flow
is straightforward, should be safe. Adding Michal to CC.


> +	if (h->surplus_huge_pages > h->nr_overcommit_huge_pages) {
>  		spin_unlock(&hugetlb_lock);
>  		put_page(page);
>  		return NULL;
> -	} else {
> -		h->surplus_huge_pages++;
> -		h->surplus_huge_pages_node[page_to_nid(page)]++;
>  	}
>  
>  out_unlock:
> -- 
> 2.20.1 (Apple Git-117)
> 
>