linux-kernel - Re: [PATCH 1/3] mm: use get_page_migratetype instead of page

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Message-ID: <20120905090955.GD11266@suse.de>
Date:	Wed, 5 Sep 2012 10:09:55 +0100
From:	Mel Gorman <mgorman@...e.de>
To:	Minchan Kim <minchan@...nel.org>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Kamezawa Hiroyuki <kamezawa.hiroyu@...fujitsu.com>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Xishi Qiu <qiuxishi@...wei.com>, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] mm: use get_page_migratetype instead of page_private

On Wed, Sep 05, 2012 at 04:26:00PM +0900, Minchan Kim wrote:
> page allocator uses set_page_private and page_private for handling
> migratetype when it frees page. Let's replace them with [set|get]
> _page_migratetype to make it more clear.
> 
> Signed-off-by: Minchan Kim <minchan@...nel.org>

Maybe it's because I'm used of setting set_page_private() in the page
allocator and what it means but I fear that it'll be very easy to confuse
get_page_migratetype() with get_pageblock_migratetype(). The former only
works while the page is in the buddy allocator. The latter can be called
at any time. I'm not against the patch as such but I'm not convinced
either :)

One nit below

> ---
>  include/linux/mm.h  |   10 ++++++++++
>  mm/page_alloc.c     |   11 +++++++----
>  mm/page_isolation.c |    2 +-
>  3 files changed, 18 insertions(+), 5 deletions(-)
> 
> diff --git a/include/linux/mm.h b/include/linux/mm.h
> index 5c76634..86d61d6 100644
> --- a/include/linux/mm.h
> +++ b/include/linux/mm.h
> @@ -249,6 +249,16 @@ struct inode;
>  #define page_private(page)		((page)->private)
>  #define set_page_private(page, v)	((page)->private = (v))
>  
> +static inline void set_page_migratetype(struct page *page, int migratetype)
> +{
> +	set_page_private(page, migratetype);
> +}
> +
> +static inline int get_page_migratetype(struct page *page)
> +{
> +	return page_private(page);
> +}
> +
>  /*
>   * FIXME: take this include out, include page-flags.h in
>   * files which need it (119 of them)
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 710d91c..103ba66 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -671,8 +671,10 @@ static void free_pcppages_bulk(struct zone *zone, int count,
>  			/* must delete as __free_one_page list manipulates */
>  			list_del(&page->lru);
>  			/* MIGRATE_MOVABLE list may include MIGRATE_RESERVEs */
> -			__free_one_page(page, zone, 0, page_private(page));
> -			trace_mm_page_pcpu_drain(page, 0, page_private(page));
> +			__free_one_page(page, zone, 0,
> +				get_page_migratetype(page));
> +			trace_mm_page_pcpu_drain(page, 0,
> +				get_page_migratetype(page));
>  		} while (--to_free && --batch_free && !list_empty(list));
>  	}
>  	__mod_zone_page_state(zone, NR_FREE_PAGES, count);
> @@ -731,6 +733,7 @@ static void __free_pages_ok(struct page *page, unsigned int order)
>  	__count_vm_events(PGFREE, 1 << order);
>  	free_one_page(page_zone(page), page, order,
>  					get_pageblock_migratetype(page));
> +
>  	local_irq_restore(flags);
>  }
>  

Unnecessary whitespace change.

> @@ -1134,7 +1137,7 @@ static int rmqueue_bulk(struct zone *zone, unsigned int order,
>  			if (!is_migrate_cma(mt) && mt != MIGRATE_ISOLATE)
>  				mt = migratetype;
>  		}
> -		set_page_private(page, mt);
> +		set_page_migratetype(page, mt);
>  		list = &page->lru;
>  	}
>  	__mod_zone_page_state(zone, NR_FREE_PAGES, -(i << order));
> @@ -1301,7 +1304,7 @@ void free_hot_cold_page(struct page *page, int cold)
>  		return;
>  
>  	migratetype = get_pageblock_migratetype(page);
> -	set_page_private(page, migratetype);
> +	set_page_migratetype(page, migratetype);
>  	local_irq_save(flags);
>  	if (unlikely(wasMlocked))
>  		free_page_mlock(page);
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index 64abb33..acf65a7 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -199,7 +199,7 @@ __test_page_isolated_in_pageblock(unsigned long pfn, unsigned long end_pfn)
>  		if (PageBuddy(page))
>  			pfn += 1 << page_order(page);
>  		else if (page_count(page) == 0 &&
> -				page_private(page) == MIGRATE_ISOLATE)
> +				get_page_migratetype(page) == MIGRATE_ISOLATE)
>  			pfn += 1;
>  		else
>  			break;

-- 
Mel Gorman
SUSE Labs
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