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

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Message-ID: <51135E33.4060508@cn.fujitsu.com>
Date:	Thu, 07 Feb 2013 15:56:35 +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>,
	Miao Xie <miaox@...fujitsu.com>
Subject: Re: [PATCH v5 01/14] memory-hotplug: try to offline the memory twice
 to avoid dependence

On 02/06/2013 10:24 PM, Glauber Costa wrote:
>>>> And one more question, a memory section is 128MB in Linux. If we reserve
>>>> part of the them for page_cgroup,
>>>> then anyone who wants to allocate a contiguous memory larger than 128MB,
>>>> it will fail, right ?
>>>> Is it OK ?
> No, it is not.
>
> Another take on this: Can't we free all the page_cgroup structure before
> we actually start removing the sections ? If we do this, we would be
> basically left with no problem at all, since when your code starts
> running we would no longer have any page_cgroup allocated.
>
> All you have to guarantee is that it happens after the memory block is
> already isolated and allocations no longer can reach it.
>
> What do you think ?

Hi Glauber,

I don't think so. We can offline some of the sections and leave the 
reset online.

For example, we store page_cgroups of memory9~11 in memory8. So when we 
offline memory8,
we free memory8's page_cgroup storing on other section, but we cannot 
free the page_cgroups
being stored in memory8 if memory9~11 are left online.

So we still need to offline memory9~11, and then offline memory8, right ?
I think it makes no difference.

Thanks. :)
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