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

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Message-ID: <alpine.DEB.2.00.1011171312590.10254@chino.kir.corp.google.com>
Date:	Wed, 17 Nov 2010 13:18:50 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Dave Hansen <dave@...ux.vnet.ibm.com>
cc:	shaohui.zheng@...el.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, 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?

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.

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.
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