linux-kernel - Re: Accounting problem of MIGRATE

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Date:	Sat, 23 Jun 2012 13:38:04 +0900
From:	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Minchan Kim <minchan@...nel.org>
CC:	undisclosed-recipients:;
	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	Aaditya Kumar <aaditya.kumar.30@...il.com>,
	Mel Gorman <mel@....ul.ie>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Accounting problem of MIGRATE_ISOLATED freed page

(2012/06/22 15:45), Minchan Kim wrote:
> On 06/22/2012 10:05 AM, Minchan Kim wrote:
>
>> Second approach which is suggested by KOSAKI is what you mentioned.
>> But the concern about second approach is how to make sure matched count increase/decrease of nr_isolated_areas.
>> I mean how to make sure nr_isolated_areas would be zero when isolation is done.
>> Of course, we can investigate all of current caller and make sure they don't make mistake
>> now. But it's very error-prone if we consider future's user.
>> So we might need test_set_pageblock_migratetype(page, MIGRATE_ISOLATE);
>
>
> It's an implementation about above approach.
>

I like this approach.


> diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h
> index bf3404e..3e9a9e1 100644
> --- a/include/linux/mmzone.h
> +++ b/include/linux/mmzone.h
> @@ -474,6 +474,11 @@ struct zone {
>           * rarely used fields:
>           */
>          const char              *name;
> +       /*
> +        * the number of MIGRATE_ISOLATE pageblock
> +        * We need this for accurate free page counting.
> +        */
> +       atomic_t                nr_migrate_isolate;
>   } ____cacheline_internodealigned_in_smp;

Isn't this counter modified only under zone->lock ?


>
>   typedef enum {
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 2c29b1c..6cb1f9f 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -219,6 +219,11 @@ EXPORT_SYMBOL(nr_online_nodes);
>
>   int page_group_by_mobility_disabled __read_mostly;
>
> +/*
> + * NOTE:
> + * Don't use set_pageblock_migratetype(page, MIGRATE_ISOLATE) direclty.
> + * Instead, use {un}set_pageblock_isolate.
> + */
>   void set_pageblock_migratetype(struct page *page, int migratetype)
>   {
>          if (unlikely(page_group_by_mobility_disabled))
> @@ -1622,6 +1627,28 @@ bool zone_watermark_ok(struct zone *z, int order, unsigned long mark,
>                                          zone_page_state(z, NR_FREE_PAGES));
>   }

I'm glad if this function can be static...Hm. With easy grep, I think it can be...

Thanks,
-Kame

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