linux-kernel - Re: [PATCH 0/2] memory-hotplug : notification of memoty block's state

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Date:	Wed, 03 Oct 2012 10:12:44 +0800
From:	Ni zhan Chen <nizhan.chen@...il.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>, x86@...nel.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	linux-acpi@...r.kernel.org, rientjes@...gle.com, liuj97@...il.com,
	len.brown@...el.com, cl@...ux.com, minchan.kim@...il.com,
	kosaki.motohiro@...fujitsu.com, wency@...fujitsu.com
Subject: Re: [PATCH 0/2] memory-hotplug : notification of memoty block's state

On 10/03/2012 09:21 AM, Yasuaki Ishimatsu wrote:
> Hi Andrew,
>
> 2012/10/03 6:42, Andrew Morton wrote:
>> On Tue, 2 Oct 2012 17:25:06 +0900
>> Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com> wrote:
>>
>>> remove_memory() offlines memory. And it is called by following two 
>>> cases:
>>>
>>> 1. echo offline >/sys/devices/system/memory/memoryXX/state
>>> 2. hot remove a memory device
>>>
>>> In the 1st case, the memory block's state is changed and the 
>>> notification
>>> that memory block's state changed is sent to userland after calling
>>> offline_memory(). So user can notice memory block is changed.
>>>
>>> But in the 2nd case, the memory block's state is not changed and the
>>> notification is not also sent to userspcae even if calling 
>>> offline_memory().
>>> So user cannot notice memory block is changed.
>>>
>>> We should also notify to userspace at 2nd case.
>>
>> These two little patches look reasonable to me.
>>
>> There's a lot of recent activity with memory hotplug!  We're in the 3.7
>> merge window now so it is not a good time to be merging new material.
>
>> Also there appear to be two teams working on it and it's unclear to me
>> how well coordinated this work is?
>
> As you know, there are two teams for developing the memory hotplug.
>   - Wen's patch-set
>     https://lkml.org/lkml/2012/9/5/201
>
>   - Lai's patch-set
>     https://lkml.org/lkml/2012/9/10/180
>
> Wen's patch-set is for removing physical memory. Now, I'm splitting the
> patch-set for reviewing more easy. If the patch-set is merged into
> linux kernel, I believe that linux on x86 can hot remove a physical
> memory device.
>
> But it is not enough since we cannot remove a memory which has kernel
> memory. If we guarantee the memory hot remove, the memory must belong
> to ZONE_MOVABLE.
>
> So Lai's patch-set tries to create a movable node that the all memory
> belongs to ZONE_MOVABLE.
>
> I think there are two chances for creating the movable node.
>   - boot time
>   - after hot add memory
>
> - boot time
>
> For creating a movable memory, linux has two kernel parameters
> (kernelcore and movablecore). But it is not enough, since even if we
> set the kernel paramter, the movable memory is distributed evenly in
> each node. So we introduce the kernelcore_max_addr boot parameter.
> The parameter limits the range of the memory used as a kernel memory.
>
> For example, the system has following nodes.
>
>     node0 : 0x40000000 - 0x80000000
>     node1 : 0x80000000 - 0xc0000000
>
> And when I want to hot remove a node1, we set 
> "kernelcore_max_addr=0x80000000".
> In doing so, kernel memory is limited within 0x80000000 and node1's
> memory belongs to ZONE_MOEVALBE. As a result, we can guarantee that
> node1 is a movable node and we always hot remove node1.
>
> - after hot add memory
>
> When hot adding memory, the memory belongs to ZONE_NORMAL and is offline.
> If we online the memory, the memory may have kernel memory. In this case,
> we cannot hot remove the memory. So we introduce the online_movable
> function. If we use the function as follow, the memory belongs to
> ZONE_MOVABLE.
>
> echo online_movable > /sys/devices/system/node/nodeX/memoryX/state
>
> So when new node is hot added and I echo "online_movale" to all hot added
> memory, the node's memory belongs to ZONE_MOVABLE. As a result, we can Y
> guarantee that the node is a movable node and we always hot remove node.

Hi Yasuaki,

This time can kernel memory allocated from ZONE_MOVABLE ?

>
> # I hope to help your understanding about our works by the information.
>
> Thanks,
> Yasuaki Ishimatsu
>
>>
>> However these two patches are pretty simple and do fix a problem, so I
>> added them to the 3.7 MM queue.
>>
>
>
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