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Date: Wed, 17 Nov 2010 13:18:50 -0800 (PST)
From: David Rientjes <rientjes@google.com>
To: Dave Hansen <dave@linux.vnet.ibm.com>
cc: shaohui.zheng@intel.com, akpm@linux-foundation.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org, haicheng.li@linux.intel.com,
        lethal@linux-sh.org, ak@linux.intel.com, shaohui.zheng@linux.intel.com,
        Haicheng Li <haicheng.li@intel.com>,
        Wu Fengguang <fengguang.wu@intel.com>, Greg KH <greg@kroah.com>
Subject: Re: [7/8,v3] NUMA Hotplug Emulator: extend memory probe interface
 to support NUMA
In-Reply-To: <1290019807.9173.3789.camel@nimitz>
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References: <20101117020759.016741414@intel.com> <20101117021000.916235444@intel.com> <1290019807.9173.3789.camel@nimitz>
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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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