linux-kernel - Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE

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Date:	Mon, 12 Aug 2013 10:23:28 -0700
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Tang Chen <imtangchen@...il.com>
CC:	Tejun Heo <tj@...nel.org>, Tang Chen <tangchen@...fujitsu.com>,
	robert.moore@...el.com, lv.zheng@...el.com, rjw@...k.pl,
	lenb@...nel.org, tglx@...utronix.de, mingo@...e.hu,
	akpm@...ux-foundation.org, trenn@...e.de, yinghai@...nel.org,
	jiang.liu@...wei.com, wency@...fujitsu.com, laijs@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, izumi.taku@...fujitsu.com,
	mgorman@...e.de, minchan@...nel.org, mina86@...a86.com,
	gong.chen@...ux.intel.com, vasilis.liaskovitis@...fitbricks.com,
	lwoodman@...hat.com, riel@...hat.com, jweiner@...hat.com,
	prarit@...hat.com, zhangyanfei@...fujitsu.com,
	yanghy@...fujitsu.com, x86@...nel.org, linux-doc@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	linux-acpi@...r.kernel.org
Subject: Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE_MOVABLE.

On 08/12/2013 10:01 AM, Tang Chen wrote:
>>
>>> I'm just thinking of a more extreme case. For example, if a machine
>>> has only one node hotpluggable, and the kernel resides in that node.
>>> Then the system has no hotpluggable node.
>>
>> Yeah, sure, then there's no way that node can be hotpluggable and the
>> right thing to do is booting up the machine and informing the userland
>> that memory is not hotpluggable.
>>
>>> If we can prevent the kernel from using hotpluggable memory, in such
>>> a machine, users can still do memory hotplug.
>>>
>>> I wanted to do it as generic as possible. But yes, finding out the
>>> nodes the kernel resides in and make it unhotpluggable can work.
>>
>> Short of being able to remap memory under the kernel, I don't think
>> this can be very generic and as a compromise trying to keep as many
>> hotpluggable nodes as possible doesn't sound too bad.
> 
> I think making one of the node hotpluggable is better. But OK, it is
> no big deal. There won't be such machine in reality, I think. :)
> 

The user may very well have configured a system with mirrored memory for
the kernel node as that will be non-hotpluggable, but not for the
others.  One can wonder how much that actually buys in real life, but
still...

	-hpa


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