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

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Message-ID: <520BCADE.2040109@gmail.com>
Date:	Wed, 14 Aug 2013 14:22:22 -0400
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Tang Chen <imtangchen@...il.com>, 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, kosaki.motohiro@...il.com
Subject: Re: [PATCH part5 0/7] Arrange hotpluggable memory as ZONE_MOVABLE.

(8/12/13 1:23 PM), H. Peter Anvin wrote:
> 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...

Note. Such system is much cheaper than full memory mirroring system. That's
one of reason why server vendors are interesting in hot plugging.

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