linux-kernel - Re: [PATCH 4/5] teach smaps_pte

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Date:	Tue, 22 Feb 2011 14:35:20 +0100
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Michael J Wolf <mjwolf@...ibm.com>, akpm@...l.org,
	Mel Gorman <mel@....ul.ie>,
	Johannes Weiner <hannes@...xchg.org>
Subject: Re: [PATCH 4/5] teach smaps_pte_range() about THP pmds

On Mon, Feb 21, 2011 at 05:53:43PM -0800, Dave Hansen wrote:
> @@ -385,8 +387,25 @@ static int smaps_pte_range(pmd_t *pmd, u
>  	pte_t *pte;
>  	spinlock_t *ptl;
>  
> -	split_huge_page_pmd(walk->mm, pmd);
> -
> +	spin_lock(&walk->mm->page_table_lock);
> +	if (pmd_trans_huge(*pmd)) {
> +		if (pmd_trans_splitting(*pmd)) {
> +			spin_unlock(&walk->mm->page_table_lock);
> +			wait_split_huge_page(vma->anon_vma, pmd);
> +		} else {
> +			smaps_pte_entry(*(pte_t *)pmd, addr,
> +					HPAGE_PMD_SIZE, walk);
> +			spin_unlock(&walk->mm->page_table_lock);
> +			return 0;
> +		}
> +	} else {
> +		spin_unlock(&walk->mm->page_table_lock);
> +	}
> +	/*
> +	 * The mmap_sem held all the way back in m_start() is what
> +	 * keeps khugepaged out of here and from collapsing things
> +	 * in here.
> +	 */

This time the locking is right and HPAGE_PMD_SIZE is used instead of
HPAGE_SIZE, thanks! I think all 5 patches can go in -mm and upstream
anytime (not mandatory for 2.6.38 but definitely we want this for
2.6.39).

BTW, Andi in his NUMA THP improvement series added a THP_SPLIT vmstat
per-cpu counter so that part removed from his series, is taken care by
him.

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