linux-kernel - Re: [PATCH 01/19] mm, thp: drop FOLL

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Date:	Tue, 25 Nov 2014 03:01:16 +0000
From:	Naoya Horiguchi <n-horiguchi@...jp.nec.com>
To:	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Dave Hansen <dave.hansen@...el.com>,
	Hugh Dickins <hughd@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Rik van Riel <riel@...hat.com>,
	Vlastimil Babka <vbabka@...e.cz>,
	Christoph Lameter <cl@...two.org>,
	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>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH 01/19] mm, thp: drop FOLL_SPLIT

On Wed, Nov 05, 2014 at 04:49:36PM +0200, Kirill A. Shutemov wrote:
> FOLL_SPLIT is used only in two places: migration and s390.
> 
> Let's replace it with explicit split and remove FOLL_SPLIT.
> 
> Signed-off-by: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> ---
...
> @@ -1246,6 +1246,11 @@ static int do_move_page_to_node_array(struct mm_struct *mm,
>  		if (!page)
>  			goto set_status;
>  
> +		if (PageTransHuge(page) && split_huge_page(page)) {
> +			err = -EBUSY;
> +			goto set_status;
> +		}
> +

This check makes split_huge_page() be called for hugetlb pages, which
triggers BUG_ON. So could you do this after if (PageHuge) block below?
And I think that we have "Node already in the right place" check afterward,
so I hope that moving down this check also helps us reduce thp splitting.

Thanks,
Naoya Horiguchi

>  		/* Use PageReserved to check for zero page */
>  		if (PageReserved(page))
>  			goto put_and_set;--
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