linux-kernel - Re: [PATCH v2 1/8] mm/page_alloc: correct to clear guard attribute in DEBUG

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Date:	Thu, 7 Aug 2014 09:46:45 +0800
From:	Zhang Yanfei <zhangyanfei@...fujitsu.com>
To:	Joonsoo Kim <iamjoonsoo.kim@....com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	Rik van Riel <riel@...hat.com>, Mel Gorman <mgorman@...e.de>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	"Srivatsa S. Bhat" <srivatsa.bhat@...ux.vnet.ibm.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	Naoya Horiguchi <n-horiguchi@...jp.nec.com>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
	Wen Congyang <wency@...fujitsu.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Michal Nazarewicz <mina86@...a86.com>,
	Laura Abbott <lauraa@...eaurora.org>,
	Heesub Shin <heesub.shin@...sung.com>,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Ritesh Harjani <ritesh.list@...il.com>,
	<t.stanislaws@...sung.com>, Gioh Kim <gioh.kim@....com>,
	<linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/8] mm/page_alloc: correct to clear guard attribute
 in DEBUG_PAGEALLOC

On 08/06/2014 03:18 PM, Joonsoo Kim wrote:
> In __free_one_page(), we check the buddy page if it is guard page.
> And, if so, we should clear guard attribute on the buddy page. But,
> currently, we clear original page's order rather than buddy one's.
> This doesn't have any problem, because resetting buddy's order
> is useless and the original page's order is re-assigned soon.
> But, it is better to correct code.
> 
> Additionally, I change (set/clear)_page_guard_flag() to
> (set/clear)_page_guard() and makes these functions do all works
> needed for guard page. This may make code more understandable.
> 
> One more thing, I did in this patch, is that fixing freepage accounting.
> If we clear guard page and link it onto isolate buddy list, we should
> not increase freepage count.
> 
> Acked-by: Vlastimil Babka <vbabka@...e.cz>
> Signed-off-by: Joonsoo Kim <iamjoonsoo.kim@....com>

Reviewed-by: Zhang Yanfei <zhangyanfei@...fujitsu.com>

> ---
>  mm/page_alloc.c |   29 ++++++++++++++++-------------
>  1 file changed, 16 insertions(+), 13 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index b99643d4..e6fee4b 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -441,18 +441,28 @@ static int __init debug_guardpage_minorder_setup(char *buf)
>  }
>  __setup("debug_guardpage_minorder=", debug_guardpage_minorder_setup);
>  
> -static inline void set_page_guard_flag(struct page *page)
> +static inline void set_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype)
>  {
>  	__set_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +	set_page_private(page, order);
> +	/* Guard pages are not available for any usage */
> +	__mod_zone_freepage_state(zone, -(1 << order), migratetype);
>  }
>  
> -static inline void clear_page_guard_flag(struct page *page)
> +static inline void clear_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype)
>  {
>  	__clear_bit(PAGE_DEBUG_FLAG_GUARD, &page->debug_flags);
> +	set_page_private(page, 0);
> +	if (!is_migrate_isolate(migratetype))
> +		__mod_zone_freepage_state(zone, (1 << order), migratetype);
>  }
>  #else
> -static inline void set_page_guard_flag(struct page *page) { }
> -static inline void clear_page_guard_flag(struct page *page) { }
> +static inline void set_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype) {}
> +static inline void clear_page_guard(struct zone *zone, struct page *page,
> +				unsigned int order, int migratetype) {}
>  #endif
>  
>  static inline void set_page_order(struct page *page, unsigned int order)
> @@ -594,10 +604,7 @@ static inline void __free_one_page(struct page *page,
>  		 * merge with it and move up one order.
>  		 */
>  		if (page_is_guard(buddy)) {
> -			clear_page_guard_flag(buddy);
> -			set_page_private(page, 0);
> -			__mod_zone_freepage_state(zone, 1 << order,
> -						  migratetype);
> +			clear_page_guard(zone, buddy, order, migratetype);
>  		} else {
>  			list_del(&buddy->lru);
>  			zone->free_area[order].nr_free--;
> @@ -876,11 +883,7 @@ static inline void expand(struct zone *zone, struct page *page,
>  			 * pages will stay not present in virtual address space
>  			 */
>  			INIT_LIST_HEAD(&page[size].lru);
> -			set_page_guard_flag(&page[size]);
> -			set_page_private(&page[size], high);
> -			/* Guard pages are not available for any usage */
> -			__mod_zone_freepage_state(zone, -(1 << high),
> -						  migratetype);
> +			set_page_guard(zone, &page[size], high, migratetype);
>  			continue;
>  		}
>  #endif
> 


-- 
Thanks.
Zhang Yanfei
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