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

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Date:	Tue, 02 Oct 2012 17:42:49 +0800
From:	Ni zhan Chen <nizhan.chen@...il.com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
CC:	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,
	akpm@...ux-foundation.org, kosaki.motohiro@...fujitsu.com,
	wency@...fujitsu.com
Subject: Re: [PATCH 0/2] memory-hotplug : notification of memoty block's state

On 10/02/2012 04:25 PM, Yasuaki Ishimatsu wrote:
> We are trying to implement a physical memory hot removing function as
> following thread.
>
> https://lkml.org/lkml/2012/9/5/201
>
> But there is not enough review to merge into linux kernel.
>
> I think there are following blockades.
>   1. no physical memory hot removable system
>   2. huge patch-set
>
> If you have a KVM system, we can get rid of 1st blockade. Because
> applying following patch, we can create memory hot removable system
> on KVM guest.
>
> http://lists.gnu.org/archive/html/qemu-devel/2012-07/msg01389.html
>
> 2nd blockade is own problem. So we try to divide huge patch into
> a small patch in each function as follows: 
>
>  - bug fix
>  - acpi framework
>  - kernel core
>
> We had already sent bug fix patches.
>
> https://lkml.org/lkml/2012/9/27/39
>
> And the patch fixes following bug.
>
> 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.,

Hi Yasuaki,

Thanks for splitting the patchset, it's more easier to review this time.
One question:

How can notify userspace? you mean function node_memory_callback or
...., but
this function basically do nothing.

>
> 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.
>
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