linux-kernel - Re: [PATCH v5 01/14] memory-hotplug: try to offline the memory twice to avoid dependence

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Date:	Thu, 10 Jan 2013 09:38:10 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Glauber Costa <glommer@...allels.com>
CC:	Wen Congyang <wency@...fujitsu.com>, akpm@...ux-foundation.org,
	rientjes@...gle.com, liuj97@...il.com, len.brown@...el.com,
	benh@...nel.crashing.org, paulus@...ba.org, cl@...ux.com,
	minchan.kim@...il.com, kosaki.motohiro@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, wujianguo@...wei.com,
	hpa@...or.com, linfeng@...fujitsu.com, laijs@...fujitsu.com,
	mgorman@...e.de, yinghai@...nel.org, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
	linux-s390@...r.kernel.org, linux-sh@...r.kernel.org,
	linux-ia64@...r.kernel.org, cmetcalf@...era.com,
	sparclinux@...r.kernel.org,
	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Subject: Re: [PATCH v5 01/14] memory-hotplug: try to offline the memory twice
 to avoid dependence

Hi Glauber,

On 01/09/2013 11:09 PM, Glauber Costa wrote:
>>
>> We try to make all page_cgroup allocations local to the node they are describing
>> now. If the memory is the first memory onlined in this node, we will allocate
>> it from the other node.
>>
>> For example, node1 has 4 memory blocks: 8-11, and we online it from 8 to 11
>> 1. memory block 8, page_cgroup allocations are in the other nodes
>> 2. memory block 9, page_cgroup allocations are in memory block 8
>>
>> So we should offline memory block 9 first. But we don't know in which order
>> the user online the memory block.
>>
>> I think we can modify memcg like this:
>> allocate the memory from the memory block they are describing
>>
>> I am not sure it is OK to do so.
>
> I don't see a reason why not.

I'm not sure, but if we do this, we could bring in a fragment for each
memory block (a memory section, 128MB, right?). Is this a problem when
we use large page (such as 1GB page) ?

Even if not, will these fragments make any bad effects ?

Thank. :)

>
> You would have to tweak a bit the lookup function for page_cgroup, but
> assuming you will always have the pfns and limits, it should be easy to do.
>
> I think the only tricky part is that today we have a single
> node_page_cgroup, and we would of course have to have one per memory
> block. My assumption is that the number of memory blocks is limited and
> likely not very big. So even a static array would do.
>
> Kamezawa, do you have any input in here?
>

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