linux-kernel - Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache

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Message-ID: <052901d23104$a6473380$f2d59a80$@alibaba-inc.com>
Date:   Fri, 28 Oct 2016 18:18:34 +0800
From:   "Hillf Danton" <hillf.zj@...baba-inc.com>
To:     "'Huang, Ying'" <ying.huang@...el.com>,
        "'Andrew Morton'" <akpm@...ux-foundation.org>
Cc:     <tim.c.chen@...el.com>, <dave.hansen@...el.com>,
        <andi.kleen@...el.com>, <aaron.lu@...el.com>, <linux-mm@...ck.org>,
        <linux-kernel@...r.kernel.org>,
        "'Andrea Arcangeli'" <aarcange@...hat.com>,
        "'Kirill A . Shutemov'" <kirill.shutemov@...ux.intel.com>,
        "'Ebru Akagunduz'" <ebru.akagunduz@...il.com>
Subject: Re: [PATCH -v4 RESEND 8/9] mm, THP, swap: Support to split THP in swap cache

On Friday, October 28, 2016 1:56 PM Huang, Ying wrote: 
> @@ -2016,10 +2021,12 @@ int page_trans_huge_mapcount(struct page *page, int *total_mapcount)
>  /* Racy check whether the huge page can be split */
>  bool can_split_huge_page(struct page *page)
>  {
> -	int extra_pins = 0;
> +	int extra_pins;
> 
>  	/* Additional pins from radix tree */
> -	if (!PageAnon(page))
> +	if (PageAnon(page))
> +		extra_pins = PageSwapCache(page) ? HPAGE_PMD_NR : 0;
> +	else
>  		extra_pins = HPAGE_PMD_NR;

extra_pins is computed in this newly added helper.

>  	return total_mapcount(page) == page_count(page) - extra_pins - 1;
>  }
> @@ -2072,7 +2079,7 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
>  			ret = -EBUSY;
>  			goto out;
>  		}
> -		extra_pins = 0;
> +		extra_pins = PageSwapCache(head) ? HPAGE_PMD_NR : 0;

It is also computed at the call site, so can we fold them into one?

>  		mapping = NULL;
>  		anon_vma_lock_write(anon_vma);
>  	} else {
> --
> 2.9.3