linux-kernel - Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory

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Date:	Thu, 31 Jan 2013 15:10:50 +0800
From:	Tang Chen <tangchen@...fujitsu.com>
To:	Simon Jeons <simon.jeons@...il.com>
CC:	akpm@...ux-foundation.org, rientjes@...gle.com,
	len.brown@...el.com, benh@...nel.crashing.org, paulus@...ba.org,
	cl@...ux.com, minchan.kim@...il.com,
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	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
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	sparclinux@...r.kernel.org
Subject: Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory

On 01/31/2013 02:19 PM, Simon Jeons wrote:
> Hi Tang,
> On Thu, 2013-01-31 at 11:31 +0800, Tang Chen wrote:
>> Hi Simon,
>>
>> Please see below. :)
>>
>> On 01/31/2013 09:22 AM, Simon Jeons wrote:
>>>
>>> Sorry, I still confuse. :(
>>> update node_states[N_NORMAL_MEMORY] to node_states[N_MEMORY] or
>>> node_states[N_NORMAL_MEMOR] present 0...ZONE_MOVABLE?
>>>
>>> node_states is what? node_states[N_NORMAL_MEMOR] or
>>> node_states[N_MEMORY]?
>>
>> Are you asking what node_states[] is ?
>>
>> node_states[] is an array of nodemask,
>>
>>       extern nodemask_t node_states[NR_NODE_STATES];
>>
>> For example, node_states[N_NORMAL_MEMOR] represents which nodes have
>> normal memory.
>> If N_MEMORY == N_HIGH_MEMORY == N_NORMAL_MEMORY, node_states[N_MEMORY] is
>> node_states[N_NORMAL_MEMOR]. So it represents which nodes have 0 ...
>> ZONE_MOVABLE.
>>
>
> Sorry, how can nodes_state[N_NORMAL_MEMORY] represents a node have 0 ...
> *ZONE_MOVABLE*, the comment of enum nodes_states said that
> N_NORMAL_MEMORY just means the node has regular memory.
>

Hi Simon,

Let's say it in this way.

If we don't have CONFIG_HIGHMEM, N_HIGH_MEMORY == N_NORMAL_MEMORY. We 
don't have a separate
macro to represent highmem because we don't have highmem.
This is easy to understand, right ?

Now, think it just like above:
If we don't have CONFIG_MOVABLE_NODE, N_MEMORY == N_HIGH_MEMORY == 
N_NORMAL_MEMORY.
This means we don't allow a node to have only movable memory, not we 
don't have movable memory.
A node could have normal memory and movable memory. So 
nodes_state[N_NORMAL_MEMORY] represents
a node have 0 ... *ZONE_MOVABLE*.

I think the point is: CONFIG_MOVABLE_NODE means we allow a node to have 
only movable memory.
So without CONFIG_MOVABLE_NODE, it doesn't mean a node cannot have 
movable memory. It means
the node cannot have only movable memory. It can have normal memory and 
movable memory.

1) With CONFIG_MOVABLE_NODE:
    N_NORMAL_MEMORY: nodes who have normal memory.
                     normal memory only
                     normal and highmem
                     normal and highmem and movablemem
                     normal and movablemem
    N_MEMORY: nodes who has memory (any memory)
                     normal memory only
                     normal and highmem
                     normal and highmem and movablemem
                     normal and movablemem ---------------- We can have 
movablemem.
                     highmem only -------------------------
                     highmem and movablemem ---------------
                     movablemem only ---------------------- We can have 
movablemem only.    ***

2) With out CONFIG_MOVABLE_NODE:
    N_MEMORY == N_NORMAL_MEMORY: (Here, I omit N_HIGH_MEMORY)
                     normal memory only
                     normal and highmem
                     normal and highmem and movablemem
                     normal and movablemem ---------------- We can have 
movablemem.
                     No movablemem only ------------------- We cannot 
have movablemem only. ***

The semantics is not that clear here. So we can only try to understand 
it from the code where
we use N_MEMORY. :)

That is my understanding of this.

Thanks. :)




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