Re: [RFC v2] memory-hotplug: remove MIGRATE_ISOLATE from free_area->free_list

[Lai Jiangshan <laijs@cn.fujitsu.com>]

On 09/06/2012 10:53 AM, Minchan Kim wrote:
> Normally, MIGRATE_ISOLATE type is used for memory-hotplug.
> But it's irony type because the pages isolated would exist
> as free page in free_area->free_list[MIGRATE_ISOLATE] so people
> can think of it as allocatable pages but it is *never* allocatable.
> It ends up confusing NR_FREE_PAGES vmstat so it would be
> totally not accurate so some of place which depend on such vmstat
> could reach wrong decision by the context.
> 
> There were already report about it.[1]
> [1] 702d1a6e, memory-hotplug: fix kswapd looping forever problem
> 
> Then, there was other report which is other problem.[2]
> [2] http://www.spinics.net/lists/linux-mm/msg41251.html
> 
> I believe it can make problems in future, too.
> So I hope removing such irony type by another design.
> 
> I hope this patch solves it and let's revert [1] and doesn't need [2].
> 
> * Changelog v1
>  * Fix from Michal's many suggestion
> 
> Cc: Michal Nazarewicz <mina86@mina86.com>
> Cc: Mel Gorman <mel@csn.ul.ie>
> Cc: Kamezawa Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
> Cc: Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>
> Cc: Wen Congyang <wency@cn.fujitsu.com>
> Cc: Konrad Rzeszutek Wilk <konrad.wilk@oracle.com>
> Signed-off-by: Minchan Kim <minchan@kernel.org>
> ---

> @@ -180,30 +287,35 @@ int undo_isolate_page_range(unsigned long start_pfn, unsigned long end_pfn,
>   * all pages in [start_pfn...end_pfn) must be in the same zone.
>   * zone->lock must be held before call this.
>   *
> - * Returns 1 if all pages in the range are isolated.
> + * Returns true if all pages in the range are isolated.
>   */
> -static int
> -__test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
> +static bool
> +__test_page_isolated_in_pageblock(unsigned long start_pfn, unsigned long end_pfn)
>  {
> +	unsigned long pfn, next_pfn;
>  	struct page *page;
>  
> -	while (pfn < end_pfn) {
> -		if (!pfn_valid_within(pfn)) {
> -			pfn++;
> -			continue;
> -		}
> -		page = pfn_to_page(pfn);
> -		if (PageBuddy(page))
> -			pfn += 1 << page_order(page);
> -		else if (page_count(page) == 0 &&
> -				page_private(page) == MIGRATE_ISOLATE)
> -			pfn += 1;
> -		else
> -			break;
> +	list_for_each_entry(page, &isolated_pages, lru) {

> +		if (&page->lru == &isolated_pages)
> +			return false;

what's the mean of this line?

> +		pfn = page_to_pfn(page);
> +		if (pfn >= end_pfn)
> +			return false;
> +		if (pfn >= start_pfn)
> +			goto found;
> +	}
> +	return false;
> +
> +	list_for_each_entry_continue(page, &isolated_pages, lru) {
> +		if (page_to_pfn(page) != next_pfn)
> +			return false;

where is next_pfn init-ed? 

> +found:
> +		pfn = page_to_pfn(page);
> +		next_pfn = pfn + (1UL << page_order(page));
> +		if (next_pfn >= end_pfn)
> +			return true;
>  	}
> -	if (pfn < end_pfn)
> -		return 0;
> -	return 1;
> +	return false;
>  }
>  
>  int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
> @@ -211,7 +323,7 @@ int test_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
>  	unsigned long pfn, flags;
>  	struct page *page;
>  	struct zone *zone;
> -	int ret;
> +	bool ret;
>  
>  	/*
>  	 * Note: pageblock_nr_page != MAX_ORDER. Then, chunks of free page
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index df7a674..bb59ff7 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -616,7 +616,6 @@ static char * const migratetype_names[MIGRATE_TYPES] = {
>  #ifdef CONFIG_CMA
>  	"CMA",
>  #endif
> -	"Isolate",
>  };
>  
>  static void *frag_start(struct seq_file *m, loff_t *pos)

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