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

From: Tang Chen <[email-masked]>
Date: Thu, 07 Feb 2013 15:56:35 +0800

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. :)