linux-kernel - Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface to support NUMA

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Message-ID: <20101118044850.GC2408@shaohui>
Date:	Thu, 18 Nov 2010 12:48:50 +0800
From:	Shaohui Zheng <shaohui.zheng@...el.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Dave Hansen <dave@...ux.vnet.ibm.com>, akpm@...ux-foundation.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	haicheng.li@...ux.intel.com, lethal@...ux-sh.org,
	ak@...ux.intel.com, shaohui.zheng@...ux.intel.com,
	Haicheng Li <haicheng.li@...el.com>,
	Wu Fengguang <fengguang.wu@...el.com>, Greg KH <greg@...ah.com>
Subject: Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface
 to support NUMA

On Wed, Nov 17, 2010 at 01:18:50PM -0800, David Rientjes wrote:
> On Wed, 17 Nov 2010, Dave Hansen wrote:
> 
> > The other thing that Greg suggested was to use configfs.  Looking back
> > on it, that makes a lot of sense.  We can do better than these "probe"
> > files.
> > 
> > In your case, it might be useful to tell the kernel to be able to add
> > memory in a node and add the node all in one go.  That'll probably be
> > closer to what the hardware will do, and will exercise different code
> > paths that the separate "add node", "then add memory" steps that you're
> > using here.
> > 
> 
> That seems like a seperate issue of moving the memory hotplug interface 
> over to configfs and that seems like it will cause a lot of userspace 
> breakage.  The memory hotplug interface can already add memory to a node 
> without using the ACPI notifier, so what does it have to do with this 
> patchset?

Agree with you, I do not suggest to implement it in this patchset.

> 
> I think what this patchset really wants to do is map offline hot-added 
> memory to a different node id before it is onlined.  It needs no 
> additional command-line interface or kconfig options, users just need to 
> physically hot-add memory at runtime or use mem= when booting to reserve 
> present memory from being used.

I already send out the implementation in another email, you can help to do
a review.

> 
> Then, export the amount of memory that is actually physically present in 
> the e820 but was truncated by mem= and allow users to hot-add the memory 
> via the probe interface.  Add a writeable 'node' file to offlined memory 
> section directories and allow it to be changed prior to online.

for memory offlining, it is a known diffcult thing, and it is not supported 
well in current kernel, so I do not suggest to provide the offline interface
in the emulator, it just take more pains. We can consider to add it when
the memory offlining works well.

-- 
Thanks & Regards,
Shaohui

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