linux-kernel - Re: [PART4 Patch v2 2/2] memory_hotplug: allow online/offline memory to result movable node

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Message-Id: <20121120142928.0aaf8fc8.akpm@linux-foundation.org>
Date:	Tue, 20 Nov 2012 14:29:28 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Wen Congyang <wency@...fujitsu.com>
Cc:	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Rob Landley <rob@...dley.net>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Lai Jiangshan <laijs@...fujitsu.com>,
	Jiang Liu <jiang.liu@...wei.com>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	Minchan Kim <minchan.kim@...il.com>,
	Mel Gorman <mgorman@...e.de>,
	David Rientjes <rientjes@...gle.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PART4 Patch v2 2/2] memory_hotplug: allow online/offline
 memory to result movable node

On Fri, 16 Nov 2012 19:58:10 +0800
Wen Congyang <wency@...fujitsu.com> wrote:

> From: Lai Jiangshan <laijs@...fujitsu.com>
> 
> Now, memory management can handle movable node or nodes which don't have
> any normal memory, so we can dynamic configure and add movable node by:
> 	online a ZONE_MOVABLE memory from a previous offline node
> 	offline the last normal memory which result a non-normal-memory-node
> 
> movable-node is very important for power-saving,
> hardware partitioning and high-available-system(hardware fault management).
> 
> ...
>
> --- a/mm/memory_hotplug.c
> +++ b/mm/memory_hotplug.c
> @@ -589,11 +589,19 @@ static int online_pages_range(unsigned long start_pfn, unsigned long nr_pages,
>  	return 0;
>  }
>  
> +#ifdef CONFIG_MOVABLE_NODE
> +/* when CONFIG_MOVABLE_NODE, we allow online node don't have normal memory */

The comment is hard to understand.  Should it read "When
CONFIG_MOVABLE_NODE, we permit onlining of a node which doesn't have
normal memory"?

> +static bool can_online_high_movable(struct zone *zone)
> +{
> +	return true;
> +}
> +#else /* #ifdef CONFIG_MOVABLE_NODE */
>  /* ensure every online node has NORMAL memory */
>  static bool can_online_high_movable(struct zone *zone)
>  {
>  	return node_state(zone_to_nid(zone), N_NORMAL_MEMORY);
>  }
> +#endif /* #ifdef CONFIG_MOVABLE_NODE */
>  
>  /* check which state of node_states will be changed when online memory */
>  static void node_states_check_changes_online(unsigned long nr_pages,
> @@ -1097,6 +1105,13 @@ check_pages_isolated(unsigned long start_pfn, unsigned long end_pfn)
>  	return offlined;
>  }
>  
> +#ifdef CONFIG_MOVABLE_NODE
> +/* when CONFIG_MOVABLE_NODE, we allow online node don't have normal memory */

Ditto, after replacing "online" with offlining".

> +static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
> +{
> +	return true;
> +}
> +#else /* #ifdef CONFIG_MOVABLE_NODE */
>  /* ensure the node has NORMAL memory if it is still online */
>  static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
>  {
> @@ -1120,6 +1135,7 @@ static bool can_offline_normal(struct zone *zone, unsigned long nr_pages)
>  	 */
>  	return present_pages == 0;
>  }
> +#endif /* #ifdef CONFIG_MOVABLE_NODE */

Please, spend more time over the accuracy and completeness of the
changelog and comments?  That will result in better and more
maintainable code.  And it results in *much* more effective code
reviewing.


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