linux-kernel - Re: [PATCHv5 08/28] khugepaged: ignore pmd tables with THP mapped with ptes

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Date:	Wed, 29 Apr 2015 17:59:21 +0200
From:	Jerome Marchand <jmarchan@...hat.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Hugh Dickins <hughd@...gle.com>
CC:	Dave Hansen <dave.hansen@...el.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Steve Capper <steve.capper@...aro.org>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Michal Hocko <mhocko@...e.cz>,
	Sasha Levin <sasha.levin@...cle.com>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org
Subject: Re: [PATCHv5 08/28] khugepaged: ignore pmd tables with THP mapped
 with ptes

On 04/23/2015 11:03 PM, Kirill A. Shutemov wrote:
> Prepare khugepaged to see compound pages mapped with pte. For now we
> won't collapse the pmd table with such pte.
> 
> khugepaged is subject for future rework wrt new refcounting.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Tested-by: Sasha Levin <sasha.levin@...cle.com>

Acked-by: Jerome Marchand <jmarchan@...hat.com>

> ---
>  mm/huge_memory.c | 6 +++++-
>  1 file changed, 5 insertions(+), 1 deletion(-)
> 
> diff --git a/mm/huge_memory.c b/mm/huge_memory.c
> index fa3d4f78b716..ffc30e4462c1 100644
> --- a/mm/huge_memory.c
> +++ b/mm/huge_memory.c
> @@ -2653,6 +2653,11 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>  		page = vm_normal_page(vma, _address, pteval);
>  		if (unlikely(!page))
>  			goto out_unmap;
> +
> +		/* TODO: teach khugepaged to collapse THP mapped with pte */
> +		if (PageCompound(page))
> +			goto out_unmap;
> +
>  		/*
>  		 * Record which node the original page is from and save this
>  		 * information to khugepaged_node_load[].
> @@ -2663,7 +2668,6 @@ static int khugepaged_scan_pmd(struct mm_struct *mm,
>  		if (khugepaged_scan_abort(node))
>  			goto out_unmap;
>  		khugepaged_node_load[node]++;
> -		VM_BUG_ON_PAGE(PageCompound(page), page);
>  		if (!PageLRU(page) || PageLocked(page) || !PageAnon(page))
>  			goto out_unmap;
>  		/*
> 



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