linux-kernel - Re: [PATCH] mm: hugetlb: bail out unmapping after serving reference page

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Message-Id: <20120223121238.b597e7e4.akpm@linux-foundation.org>
Date:	Thu, 23 Feb 2012 12:12:38 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Hillf Danton <dhillf@...il.com>
Cc:	Linux-MM <linux-mm@...ck.org>, LKML <linux-kernel@...r.kernel.org>,
	Michal Hocko <mhocko@...e.cz>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>
Subject: Re: [PATCH] mm: hugetlb: bail out unmapping after serving reference
 page

On Thu, 23 Feb 2012 21:05:41 +0800
Hillf Danton <dhillf@...il.com> wrote:

> and a follow-up cleanup also attached.

Please, never put more than one patches in an email - it is rather a
pain to manually unpick everything.

> When unmapping given VM range, a couple of code duplicate, such as pte_page()
> and huge_pte_none(), so a cleanup needed to compact them together.
> 
> Signed-off-by: Hillf Danton <dhillf@...il.com>
> ---
> 
> --- a/mm/hugetlb.c	Thu Feb 23 20:13:06 2012
> +++ b/mm/hugetlb.c	Thu Feb 23 20:30:16 2012
> @@ -2245,16 +2245,23 @@ void __unmap_hugepage_range(struct vm_ar
>  		if (huge_pmd_unshare(mm, &address, ptep))
>  			continue;
> 
> +		pte = huge_ptep_get(ptep);
> +		if (huge_pte_none(pte))
> +			continue;
> +
> +		/*
> +		 * HWPoisoned hugepage is already unmapped and dropped reference
> +		 */
> +		if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
> +			continue;
> +
> +		page = pte_page(pte);
>  		/*
>  		 * If a reference page is supplied, it is because a specific
>  		 * page is being unmapped, not a range. Ensure the page we
>  		 * are about to unmap is the actual page of interest.
>  		 */
>  		if (ref_page) {
> -			pte = huge_ptep_get(ptep);
> -			if (huge_pte_none(pte))
> -				continue;
> -			page = pte_page(pte);
>  			if (page != ref_page)
>  				continue;
> 
> @@ -2267,16 +2274,6 @@ void __unmap_hugepage_range(struct vm_ar
>  		}
> 
>  		pte = huge_ptep_get_and_clear(mm, address, ptep);
> -		if (huge_pte_none(pte))
> -			continue;
> -
> -		/*
> -		 * HWPoisoned hugepage is already unmapped and dropped reference
> -		 */
> -		if (unlikely(is_hugetlb_entry_hwpoisoned(pte)))
> -			continue;
> -
> -		page = pte_page(pte);
>  		if (pte_dirty(pte))
>  			set_page_dirty(page);
>  		list_add(&page->lru, &page_list);

This changes behaviour when ref_page refers to a hwpoisoned page.
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