linux-kernel - Re: [PATCH 2/7] mm/balloon_compaction: keep ballooned pages away from normal migration path

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Date:	Wed, 20 Aug 2014 20:33:09 -0300
From:	Rafael Aquini <aquini@...hat.com>
To:	Konstantin Khlebnikov <k.khlebnikov@...sung.com>
Cc:	linux-mm@...ck.org, Andrew Morton <akpm@...ux-foundation.org>,
	Sasha Levin <sasha.levin@...cle.com>,
	Andrey Ryabinin <ryabinin.a.a@...il.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/7] mm/balloon_compaction: keep ballooned pages away
 from normal migration path

On Wed, Aug 20, 2014 at 07:04:40PM +0400, Konstantin Khlebnikov wrote:
> Proper testing shows yet another problem in balloon migration: it works only
> once for each page. balloon_page_movable() check page flags and page_count.
> In __unmap_and_move page is locked, reference counter is elevated, so
> balloon_page_movable() _always_ fails here. As result in __unmap_and_move()
> migration goes to the normal migration path.
> 
> Balloon ->migratepage() is so special, it returns MIGRATEPAGE_BALLOON_SUCCESS
> instead of MIGRATEPAGE_SUCCESS. After that in move_to_new_page() successfully
> migrated page got NULL into its mapping pointer and loses connectivity with
> balloon and ability for further migration.
> 
> It's safe to use __is_movable_balloon_page here: page is isolated and pinned.
> 
> Signed-off-by: Konstantin Khlebnikov <k.khlebnikov@...sung.com>
> Cc: stable <stable@...r.kernel.org> # v3.8
> ---
>  mm/migrate.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/migrate.c b/mm/migrate.c
> index f78ec9b..161d044 100644
> --- a/mm/migrate.c
> +++ b/mm/migrate.c
> @@ -873,7 +873,7 @@ static int __unmap_and_move(struct page *page, struct page *newpage,
>  		}
>  	}
>  
> -	if (unlikely(balloon_page_movable(page))) {
> +	if (unlikely(__is_movable_balloon_page(page))) {
>  		/*
>  		 * A ballooned page does not need any special attention from
>  		 * physical to virtual reverse mapping procedures.
> 
Acked-by: Rafael Aquini <aquini@...hat.com>
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