# Re: \[PATCH v6 00/15\] memory-hotplug: hot-remove physical memory

- From: Tang Chen \<hidden\>
- Date: 2013-01-31 07:11:59 
- List: linuxppc-dev
- Page: https://ratatoskr.run/linuxppc-dev/2013/01/3993849
- Thread: https://ratatoskr.run/linux-mm/2013/01/3980481/t.md

```text
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. :)
```