linux-kernel - Re: [3/8,v3] NUMA Hotplug Emulator: Userland interface to hotplug-add fake offlined nodes.

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Message-ID: <alpine.DEB.2.00.1011170010430.17408@chino.kir.corp.google.com>
Date:	Wed, 17 Nov 2010 00:16:52 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Shaohui Zheng <shaohui.zheng@...el.com>
cc:	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, Dave Hansen <haveblue@...ibm.com>,
	Christoph Lameter <cl@...ux-foundation.org>,
	Haicheng Li <haicheng.li@...el.com>
Subject: Re: [3/8,v3] NUMA Hotplug Emulator: Userland interface to hotplug-add
 fake offlined nodes.

On Wed, 17 Nov 2010, shaohui.zheng@...el.com wrote:

> From: Haicheng Li <haicheng.li@...el.com>
> 
> Add a sysfs entry "probe" under /sys/devices/system/node/:
> 
>  - to show all fake offlined nodes:
>     $ cat /sys/devices/system/node/probe
> 
>  - to hotadd a fake offlined node, e.g. nodeid is N:
>     $ echo N > /sys/devices/system/node/probe
> 

This would be much more powerful if we just reserved an amount of memory 
at boot and then allowed users to hot-add a given amount with an 
non-online node id.  Then we can test nodes of various sizes rather than 
being statically committed at boot.

This should be fairly straight-forward by faking 
ACPI_SRAT_MEM_HOT_PLUGGABLE entries, for example.

> Index: linux-hpe4/mm/Kconfig
> ===================================================================
> --- linux-hpe4.orig/mm/Kconfig	2010-11-15 17:13:02.443461606 +0800
> +++ linux-hpe4/mm/Kconfig	2010-11-15 17:21:05.535335091 +0800
> @@ -147,6 +147,21 @@
>  	depends on MEMORY_HOTPLUG && ARCH_ENABLE_MEMORY_HOTREMOVE
>  	depends on MIGRATION
>  
> +config NUMA_HOTPLUG_EMU
> +	bool "NUMA hotplug emulator"
> +	depends on X86_64 && NUMA && MEMORY_HOTPLUG
> +
> +	---help---
> +
> +config NODE_HOTPLUG_EMU
> +	bool "Node hotplug emulation"
> +	depends on NUMA_HOTPLUG_EMU && MEMORY_HOTPLUG
> +	---help---
> +	  Enable Node hotplug emulation. The machine will be setup with
> +	  hidden virtual nodes when booted with "numa=hide=N*size", where
> +	  N is the number of hidden nodes, size is the memory size per
> +	  hidden node. This is only useful for debugging.
> +

That's clearly wrong, but I don't see why this needs to be a new Kconfig 
option to begin with, can't we enable all of this functionality by default 
under CONFIG_NUMA_EMU && CONFIG_MEMORY_HOTPLUG?
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