linux-kernel - Re: [PATCH 3/6] mm: add is_migrate_isolate_page_nolock() for cases where locking is undesirable

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Date:	Wed, 5 Mar 2014 09:39:08 +0900
From:	Joonsoo Kim <iamjoonsoo.kim@....com>
To:	Vlastimil Babka <vbabka@...e.cz>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Mel Gorman <mgorman@...e.de>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, Rik van Riel <riel@...hat.com>,
	Johannes Weiner <hannes@...xchg.org>,
	Minchan Kim <minchan@...nel.org>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH 3/6] mm: add is_migrate_isolate_page_nolock() for cases
 where locking is undesirable

On Fri, Feb 28, 2014 at 03:15:01PM +0100, Vlastimil Babka wrote:
> This patch complements the addition of get_pageblock_migratetype_nolock() for
> the case where is_migrate_isolate_page() cannot be called with zone->lock held.
> A race with set_pageblock_migratetype() may be detected, in which case a caller
> supplied argument is returned.
> 
> Signed-off-by: Vlastimil Babka <vbabka@...e.cz>
> ---
>  include/linux/page-isolation.h | 24 ++++++++++++++++++++++++
>  mm/hugetlb.c                   |  2 +-
>  2 files changed, 25 insertions(+), 1 deletion(-)
> 
> diff --git a/include/linux/page-isolation.h b/include/linux/page-isolation.h
> index 3fff8e7..f7bd491 100644
> --- a/include/linux/page-isolation.h
> +++ b/include/linux/page-isolation.h
> @@ -2,10 +2,30 @@
>  #define __LINUX_PAGEISOLATION_H
>  
>  #ifdef CONFIG_MEMORY_ISOLATION
> +/*
> + * Should be called only with zone->lock held. In cases where locking overhead
> + * is undesirable, consider the _nolock version.
> + */
>  static inline bool is_migrate_isolate_page(struct page *page)
>  {
>  	return get_pageblock_migratetype(page) == MIGRATE_ISOLATE;
>  }
> +/*
> + * When called without zone->lock held, a race with set_pageblock_migratetype
> + * may result in bogus values. The race may be detected, in which case the
> + * value of race_fallback argument is returned. For details, see
> + * get_pageblock_migratetype_nolock().
> + */
> +static inline bool is_migrate_isolate_page_nolock(struct page *page,
> +		bool race_fallback)
> +{
> +	int migratetype = get_pageblock_migratetype_nolock(page, MIGRATE_TYPES);
> +
> +	if (unlikely(migratetype == MIGRATE_TYPES))
> +		return race_fallback;
> +
> +	return migratetype == MIGRATE_ISOLATE;
> +}
>  static inline bool is_migrate_isolate(int migratetype)
>  {
>  	return migratetype == MIGRATE_ISOLATE;
> @@ -15,6 +35,10 @@ static inline bool is_migrate_isolate_page(struct page *page)
>  {
>  	return false;
>  }
> +static inline bool is_migrate_isolate_page_nolock(struct page *page)
> +{
> +	return false;
> +}
>  static inline bool is_migrate_isolate(int migratetype)
>  {
>  	return false;

Nitpick.
You need race_fallback parameter for is_migrate_isolate_page_nolock().

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