linux-kernel - Re: [PATCH] THP: Use explicit memory barrier

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Date:	Thu, 4 Apr 2013 15:45:45 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Hugh Dickins <hughd@...gle.com>,
	David Rientjes <rientjes@...gle.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Mel Gorman <mgorman@...e.de>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Subject: Re: [PATCH] THP: Use explicit memory barrier

On Wed, Apr 03, 2013 at 09:14:01AM +0900, Minchan Kim wrote:
>  	clear_huge_page(page, haddr, HPAGE_PMD_NR);
> +	/*
> +	 * The memory barrier inside __SetPageUptodate makes sure that
> +	 * clear_huge_page writes become visible after the set_pmd_at()

s/after/before/

> +	 * write.
> +	 */
>  	__SetPageUptodate(page);
>  
>  	spin_lock(&mm->page_table_lock);
> @@ -724,12 +729,6 @@ static int __do_huge_pmd_anonymous_page(struct mm_struct *mm,
>  	} else {
>  		pmd_t entry;
>  		entry = mk_huge_pmd(page, vma);
> -		/*
> -		 * The spinlocking to take the lru_lock inside
> -		 * page_add_new_anon_rmap() acts as a full memory
> -		 * barrier to be sure clear_huge_page writes become
> -		 * visible after the set_pmd_at() write.
> -		 */
>  		page_add_new_anon_rmap(page, vma, haddr);
>  		set_pmd_at(mm, haddr, pmd, entry);
>  		pgtable_trans_huge_deposit(mm, pgtable);
> diff --git a/mm/memory.c b/mm/memory.c
> index 494526a..d0da51e 100644
> --- a/mm/memory.c
> +++ b/mm/memory.c
> @@ -3196,6 +3196,11 @@ static int do_anonymous_page(struct mm_struct *mm, struct vm_area_struct *vma,
>  	page = alloc_zeroed_user_highpage_movable(vma, address);
>  	if (!page)
>  		goto oom;
> +	/*
> +	 * The memory barrier inside __SetPageUptodate makes sure that
> +	 * preceeding stores to the page contents become visible after
> +	 * the set_pte_at() write.
> +	 */

s/after/before/

After the above correction it looks nice cleanup, thanks!

Acked-by: Andrea Arcangeli <aarcange@...hat.com>

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