linux-kernel - Re: [PATCH v2 0/5] Add movablecore

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Message-ID: <50B4B6BE.3000902@cn.fujitsu.com>
Date:	Tue, 27 Nov 2012 20:49:02 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Bob Liu <lliubbo@...il.com>
CC:	hpa@...or.com, akpm@...ux-foundation.org, rob@...dley.net,
	isimatu.yasuaki@...fujitsu.com, laijs@...fujitsu.com,
	wency@...fujitsu.com, linfeng@...fujitsu.com, jiang.liu@...wei.com,
	yinghai@...nel.org, kosaki.motohiro@...fujitsu.com,
	minchan.kim@...il.com, mgorman@...e.de, rientjes@...gle.com,
	rusty@...tcorp.com.au, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org, linux-doc@...r.kernel.org,
	m.szyprowski@...sung.com
Subject: Re: [PATCH v2 0/5] Add movablecore_map boot option

On 11/27/2012 08:09 PM, Bob Liu wrote:
> On Tue, Nov 27, 2012 at 4:29 PM, Tang Chen<tangchen@...fujitsu.com>  wrote:
>> Hi Liu,
>>
>> This feature is used in memory hotplug.
>>
>> In order to implement a whole node hotplug, we need to make sure the
>> node contains no kernel memory, because memory used by kernel could
>> not be migrated. (Since the kernel memory is directly mapped,
>> VA = PA + __PAGE_OFFSET. So the physical address could not be changed.)
>>
>> User could specify all the memory on a node to be movable, so that the
>> node could be hot-removed.
>>
>
> Thank you for your explanation. It's reasonable.
>
> But i think it's a bit duplicated with CMA, i'm not sure but maybe we
> can combine it with CMA which already in mainline?
>
Hi Liu,

Thanks for your advice. :)

CMA is Contiguous Memory Allocator, right?  What I'm trying to do is
controlling where is the start of ZONE_MOVABLE of each node. Could
CMA do this job ?

And also, after a short investigation, CMA seems need to base on
memblock. But we need to limit memblock not to allocate memory on
ZONE_MOVABLE. As a result, we need to know the ranges before memblock
could be used. I'm afraid we still need an approach to get the ranges,
such as a boot option, or from static ACPI tables such as SRAT/MPST.

I'm don't know much about CMA for now. So if you have any better idea,
please share with us, thanks. :)


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