linux-kernel - Re: [PATCH] mm, hugetlb: correct missing private flag clearing

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Date:	Mon, 30 Sep 2013 14:35:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
Cc:	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Michal Hocko <mhocko@...e.cz>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Hugh Dickins <hughd@...gle.com>,
	Davidlohr Bueso <davidlohr.bueso@...com>,
	David Gibson <david@...son.dropbear.id.au>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Joonsoo Kim <js1304@...il.com>,
	Wanpeng Li <liwanp@...ux.vnet.ibm.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Hillf Danton <dhillf@...il.com>
Subject: Re: [PATCH] mm, hugetlb: correct missing private flag clearing

On Mon, 30 Sep 2013 16:59:44 +0900 Joonsoo Kim <iamjoonsoo.kim@....com> wrote:

> We should clear the page's private flag when returing the page to
> the page allocator or the hugepage pool. This patch fixes it.
> 
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>
> ---
> Hello, Andrew.
> 
> I sent the new version of commit ('07443a8') before you did pull request,
> but it isn't included. It may be losted :)
> So I send this fix. IMO, this is good for v3.12.
> 
> Thanks.
> 
> diff --git a/mm/hugetlb.c b/mm/hugetlb.c
> index b49579c..691f226 100644
> --- a/mm/hugetlb.c
> +++ b/mm/hugetlb.c
> @@ -653,6 +653,7 @@ static void free_huge_page(struct page *page)
>  	BUG_ON(page_count(page));
>  	BUG_ON(page_mapcount(page));
>  	restore_reserve = PagePrivate(page);
> +	ClearPagePrivate(page);
>  

You describe it as a fix, but what does it fix?  IOW, what are the
user-visible effects of the change?

update_and_free_page() already clears PG_private, but afaict the bit
remains unaltered if free_huge_page() takes the enqueue_huge_page()
route.

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