linux-kernel - Re: [PATCH 2/2] mm: page_isolation: fix zone

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Message-ID: <20141106084907.GA29209@js1304-P5Q-DELUXE>
Date:	Thu, 6 Nov 2014 17:49:07 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Weijie Yang <weijie.yang@...sung.com>
Cc:	kamezawa.hiroyu@...fujitsu.com, 'Minchan Kim' <minchan@...nel.org>,
	'Andrew Morton' <akpm@...ux-foundation.org>, mgorman@...e.de,
	mina86@...a86.com, 'linux-kernel' <linux-kernel@...r.kernel.org>,
	'Linux-MM' <linux-mm@...ck.org>,
	'Weijie Yang' <weijie.yang.kh@...il.com>
Subject: Re: [PATCH 2/2] mm: page_isolation: fix zone_freepage accounting

On Thu, Nov 06, 2014 at 04:09:08PM +0800, Weijie Yang wrote:
> If race between isolatation and allocation happens, we could need to move
> some freepages to MIGRATE_ISOLATE in __test_page_isolated_in_pageblock().
> The current code ignores the zone_freepage accounting after the move,
> which cause the zone NR_FREE_PAGES and NR_FREE_CMA_PAGES statistics incorrect.
> 
> This patch fixes this rare issue.

Hello,

After "fix freepage count problems in memory isolation" merged, this race
should not happen. I have to remove it in that patchset, but, I
forgot to remove it. Please remove this race handling code completely and
tag with stable. If we don't remove it, there is errornous situation
because get_freepage_migratetype() could return invalid migratetype
although the page is on the correct buddy list. So, we regard
no race situation as race one.

Thanks.

> 
> Signed-off-by: Weijie Yang <weijie.yang@...sung.com>
> ---
>  mm/page_isolation.c |    5 ++++-
>  1 files changed, 4 insertions(+), 1 deletions(-)
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 3ddc8b3..15b51de 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -193,12 +193,15 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn,
>  			 * is MIGRATE_ISOLATE. Catch it and move the page into
>  			 * MIGRATE_ISOLATE list.
>  			 */
> -			if (get_freepage_migratetype(page) != MIGRATE_ISOLATE) {
> +			int migratetype = get_freepage_migratetype(page);
> +			if (migratetype != MIGRATE_ISOLATE) {
>  				struct page *end_page;
>  
>  				end_page = page + (1 << page_order(page)) - 1;
>  				move_freepages(page_zone(page), page, end_page,
>  						MIGRATE_ISOLATE);
> +				__mod_zone_freepage_state(zone,
> +					-(1 << page_order(page)), migratetype);
>  			}
>  			pfn += 1 << page_order(page);
>  		}
> -- 
> 1.7.0.4
> 
> 
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