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

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Date:	Thu, 31 Jan 2013 02:17:08 -0600
From:	Simon Jeons <simon.jeons@...il.com>
To:	Tang Chen <tangchen@...fujitsu.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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	yinghai@...nel.org, glommer@...allels.com, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, linux-acpi@...r.kernel.org,
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	sparclinux@...r.kernel.org
Subject: Re: [PATCH v6 00/15] memory-hotplug: hot-remove physical memory

Hi Tang,
On Thu, 2013-01-31 at 15:10 +0800, Tang Chen wrote:
> 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 for your clarify, very clear now. :)

> 
> Thanks. :)
> 
> 
> 
> 
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