linux-kernel - Re: [PATCH v5 0/5] Add movablecore

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Message-ID: <50F79422.6090405@zytor.com>
Date:	Wed, 16 Jan 2013 22:03:14 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	"Luck, Tony" <tony.luck@...el.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	"jiang.liu@...wei.com" <jiang.liu@...wei.com>,
	"wujianguo@...wei.com" <wujianguo@...wei.com>,
	"wency@...fujitsu.com" <wency@...fujitsu.com>,
	"laijs@...fujitsu.com" <laijs@...fujitsu.com>,
	"linfeng@...fujitsu.com" <linfeng@...fujitsu.com>,
	"yinghai@...nel.org" <yinghai@...nel.org>,
	"rob@...dley.net" <rob@...dley.net>,
	"kosaki.motohiro@...fujitsu.com" <kosaki.motohiro@...fujitsu.com>,
	"minchan.kim@...il.com" <minchan.kim@...il.com>,
	"mgorman@...e.de" <mgorman@...e.de>,
	"rientjes@...gle.com" <rientjes@...gle.com>,
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	"rusty@...tcorp.com.au" <rusty@...tcorp.com.au>,
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	"glommer@...allels.com" <glommer@...allels.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>
Subject: Re: [PATCH v5 0/5] Add movablecore_map boot option

On 01/16/2013 09:08 PM, Yasuaki Ishimatsu wrote:
>
> I thought about the method of specifying the node. But I think
> this method is inconvenience. Node number is decided by OS.
> So the number is changed easily.
>
> for example:
>
> o exmaple 1
>    System has 3 nodes:
>    node0, node1, node2
>
>    When user remove node1, the system has:
>    node0, node2
>
>    But after rebooting the system, the system has:
>    node0, node1
>
>    So node2 becomes node1.
>
> o example 2:
>    System has 2 nodes:
>    0x40000000 - 0x7fffffff : node0
>    0xc0000000 - 0xffffffff : node1
>
>    When user add a node wchih memory range is [0x80000000 - 0xbfffffff],
>    system has:
>    0x40000000 - 0x7fffffff : node0
>    0xc0000000 - 0xffffffff : node1
>    0x80000000 - 0xbfffffff : node2
>
>    But after rebooting the system, the system's node may become:
>    0x40000000 - 0x7fffffff : node0
>    0x80000000 - 0xbfffffff : node1
>    0xc0000000 - 0xffffffff : node2
>
>    So node nunber is changed.
>
> Specifying node number may be easy method than specifying memory
> range. But if user uses node number for specifying removable memory,
> user always need to care whether node number is changed or not at
> every hotplug operation.
>


Well, there are only two options:

1. The user doesn't care which nodes are movable.  In that case, the 
user may just want to specify a target as a percentage of memory to make 
movable -- effectively a "slider" on the performance vs. reliability 
spectrum.  The kernel can then assign nodes arbitrarily.

2. If the user *does* care which nodes are movable, then the user needs 
to be able to specify that *in a way that makes sense to the user*. 
This may mean involving the DMI information as well as SRAT in order to 
get "silk screen" type information out.

	-hpa



-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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