linux-kernel - Re: [PART4 Patch v2 1/2] numa: add CONFIG_MOVABLE

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Message-ID: <50AC4A1B.9020908@cn.fujitsu.com>
Date:	Wed, 21 Nov 2012 11:27:23 +0800
From:	Wen Congyang <wency@...fujitsu.com>
To:	Andrew Morton <akpm@...ux-foundation.org>
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 1/2] numa: add CONFIG_MOVABLE_NODE for movable-dedicated
 node

At 11/21/2012 06:25 AM, Andrew Morton Wrote:
> On Fri, 16 Nov 2012 19:58:09 +0800
> Wen Congyang <wency@...fujitsu.com> wrote:
> 
>> From: Lai Jiangshan <laijs@...fujitsu.com>
>>
>> All are prepared, we can actually introduce N_MEMORY.
>> add CONFIG_MOVABLE_NODE make we can use it for movable-dedicated node
> 
> This description is far too short on details.
> 
> I grabbed this from the [0/n] email:
> 
> : We need a node which only contains movable memory.  This feature is very
> : important for node hotplug.  If a node has normal/highmem, the memory may
> : be used by the kernel and can't be offlined.  If the node only contains
> : movable memory, we can offline the memory and the node.
> 
> which helps a bit, but it's still pretty thin.
> 
> Why is this option made configurable?  Why not enable it unconditionally?
> 
> Please send a patch which adds the Kconfig help text for
> CONFIG_MOVABLE_NODE.  Let's make that text nice and detailed.
> 
> The name MOVABLE_NODE is not a good one.  It means "a node which is
> movable", whereas the concept is actually "a node whcih contains only
> movable memory".  I suppose we could change it to something like
> CONFIG_MOVABLE_MEMORY_ONLY_NODE or similar.  But I suppose that
> CONFIG_MOVABLE_NODE is good enough, as long as it is well-described in
> associated comments or help text.  This is not the case at present.
> 
>> +#ifdef CONFIG_MOVABLE_NODE
>> +	N_MEMORY,		/* The node has memory(regular, high, movable) */
>> +#else
> 
> I think the comment should be "The node has only movable memory"?

No, the comment is right. In the kernel, we need the following two
mask:
1. the node contains memory that the kernel can use(N_HIGH_MEMORY)
2. the node contains memory (N_MEMORY)

There is no code need the mask: the node contains only movable memory
now.

Thanks
Wen Congyang

> 
> 
> 

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