linux-kernel - Re: [PATCH v2 2/2] mm: clean up __count_immobile

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Message-ID: <4FD93B1F.3010909@kernel.org>
Date:	Thu, 14 Jun 2012 10:15:11 +0900
From:	Minchan Kim <minchan@...nel.org>
To:	undisclosed-recipients:;
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Andrea Arcangeli <aarcange@...hat.com>,
	Mel Gorman <mgorman@...e.de>, Michal Hocko <mhocko@...e.cz>,
	Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Subject: Re: [PATCH v2 2/2] mm: clean up __count_immobile_pages

Missing Bartlomiej, Sorry!

On 06/14/2012 10:12 AM, Minchan Kim wrote:

> __count_immobile_pages naming is rather awkward.
> This patch changes function name more clear and add comment.
> 
> * changelog from v1
>   - write down page flag race in function comment
>   - commit change log change
> 
> Cc: Andrea Arcangeli <aarcange@...hat.com>
> Cc: Mel Gorman <mgorman@...e.de>
> Cc: Michal Hocko <mhocko@...e.cz>
> Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
> Signed-off-by: Minchan Kim <minchan@...nel.org>
> ---
>  mm/page_alloc.c |   34 ++++++++++++++++++----------------
>  1 file changed, 18 insertions(+), 16 deletions(-)
> 
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 543cc2d..dc7f8c5 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -5467,26 +5467,28 @@ void set_pageblock_flags_group(struct page *page, unsigned long flags,
>  }
>  
>  /*
> - * This is designed as sub function...plz see page_isolation.c also.
> - * set/clear page block's type to be ISOLATE.
> - * page allocater never alloc memory from ISOLATE block.
> + * This function checks whether pageblock includes unmovable pages or not.
> + * If @count is not zero, it is okay to include less @count unmovable pages
> + *
> + * PageLRU check wihtout isolation or lru_lock could race so that
> + * MIGRATE_MOVABLE block might include unmovable pages. It means you can't
> + * expect this function should be exact.
>   */
> -
> -static int
> -__count_immobile_pages(struct zone *zone, struct page *page, int count)
> +static bool
> +__has_unmovable_pages(struct zone *zone, struct page *page, int count)
>  {
>  	unsigned long pfn, iter, found;
>  	int mt;
>  
>  	/*
>  	 * For avoiding noise data, lru_add_drain_all() should be called
> -	 * If ZONE_MOVABLE, the zone never contains immobile pages
> +	 * If ZONE_MOVABLE, the zone never contains unmovable pages
>  	 */
>  	if (zone_idx(zone) == ZONE_MOVABLE)
> -		return true;
> +		return false;
>  	mt = get_pageblock_migratetype(page);
>  	if (mt == MIGRATE_MOVABLE || is_migrate_cma(mt))
> -		return true;
> +		return false;
>  
>  	pfn = page_to_pfn(page);
>  	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
> @@ -5524,9 +5526,9 @@ __count_immobile_pages(struct zone *zone, struct page *page, int count)
>  		 * page at boot.
>  		 */
>  		if (found > count)
> -			return false;
> +			return true;
>  	}
> -	return true;
> +	return false;
>  }
>  
>  bool is_pageblock_removable_nolock(struct page *page)
> @@ -5550,7 +5552,7 @@ bool is_pageblock_removable_nolock(struct page *page)
>  			zone->zone_start_pfn + zone->spanned_pages <= pfn)
>  		return false;
>  
> -	return __count_immobile_pages(zone, page, 0);
> +	return !__has_unmovable_pages(zone, page, 0);
>  }
>  
>  int set_migratetype_isolate(struct page *page)
> @@ -5589,12 +5591,12 @@ int set_migratetype_isolate(struct page *page)
>  	 * FIXME: Now, memory hotplug doesn't call shrink_slab() by itself.
>  	 * We just check MOVABLE pages.
>  	 */
> -	if (__count_immobile_pages(zone, page, arg.pages_found))
> +	if (!__has_unmovable_pages(zone, page, arg.pages_found))
>  		ret = 0;
> -
>  	/*
> -	 * immobile means "not-on-lru" paes. If immobile is larger than
> -	 * removable-by-driver pages reported by notifier, we'll fail.
> +	 * Unmovable means "not-on-lru" pages. If Unmovable pages are
> +	 * larger than removable-by-driver pages reported by notifier,
> +	 * we'll fail.
>  	 */
>  
>  out:



-- 
Kind regards,
Minchan Kim
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