linux-kernel - Re: [PATCH v2] mm/hotplug, x86: Disable ARCH_MEMORY

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Date:	Mon, 22 Jul 2013 18:45:37 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org,
	linux-kernel@...r.kernel.org, x86@...nel.org, dave@...1.net,
	kosaki.motohiro@...il.com, tangchen@...fujitsu.com,
	vasilis.liaskovitis@...fitbricks.com
Subject: Re: [PATCH v2] mm/hotplug, x86: Disable ARCH_MEMORY_PROBE by default

On Tue, 2013-07-23 at 09:24 +0900, Yasuaki Ishimatsu wrote:
> (2013/07/20 2:47), Toshi Kani wrote:
> > CONFIG_ARCH_MEMORY_PROBE enables /sys/devices/system/memory/probe
> > interface, which allows a given memory address to be hot-added as
> > follows. (See Documentation/memory-hotplug.txt for more detail.)
> > 
> > # echo start_address_of_new_memory > /sys/devices/system/memory/probe
> > 
> > This probe interface is required on powerpc. On x86, however, ACPI
> > notifies a memory hotplug event to the kernel, which performs its
> > hotplug operation as the result. Therefore, regular users do not need
> > this interface on x86. This probe interface is also error-prone and
> > misleading that the kernel blindly adds a given memory address without
> > checking if the memory is present on the system; no probing is done
> > despite of its name. The kernel crashes when a user requests to online
> > a memory block that is not present on the system. This interface is
> > currently used for testing as it can fake a hotplug event.
> > 
> > This patch disables CONFIG_ARCH_MEMORY_PROBE by default on x86, adds
> > its Kconfig menu entry on x86, and clarifies its use in Documentation/
> > memory-hotplug.txt.
> > 
> > Signed-off-by: Toshi Kani <toshi.kani@...com>
> 
> Reviewed-by: Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>

Great!  Thanks Yasuaki!
-Toshi


> 
> Thanks,
> Yasuaki Ishimatsu
> 
> > ---
> >   Documentation/memory-hotplug.txt |   16 +++++++++-------
> >   arch/x86/Kconfig                 |    7 ++++++-
> >   2 files changed, 15 insertions(+), 8 deletions(-)
> > 
> > diff --git a/Documentation/memory-hotplug.txt b/Documentation/memory-hotplug.txt
> > index 8e5eacb..8fd254c 100644
> > --- a/Documentation/memory-hotplug.txt
> > +++ b/Documentation/memory-hotplug.txt
> > @@ -210,13 +210,15 @@ If memory device is found, memory hotplug code will be called.
> >   
> >   4.2 Notify memory hot-add event by hand
> >   ------------
> > -In some environments, especially virtualized environment, firmware will not
> > -notify memory hotplug event to the kernel. For such environment, "probe"
> > -interface is supported. This interface depends on CONFIG_ARCH_MEMORY_PROBE.
> > -
> > -Now, CONFIG_ARCH_MEMORY_PROBE is supported only by powerpc but it does not
> > -contain highly architecture codes. Please add config if you need "probe"
> > -interface.
> > +On powerpc, the firmware does not notify a memory hotplug event to the kernel.
> > +Therefore, "probe" interface is supported to notify the event to the kernel.
> > +This interface depends on CONFIG_ARCH_MEMORY_PROBE.
> > +
> > +CONFIG_ARCH_MEMORY_PROBE is supported on powerpc only. On x86, this config
> > +option is disabled by default since ACPI notifies a memory hotplug event to
> > +the kernel, which performs its hotplug operation as the result. Please
> > +enable this option if you need the "probe" interface for testing purposes
> > +on x86.
> >   
> >   Probe interface is located at
> >   /sys/devices/system/memory/probe
> > diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
> > index b32ebf9..408ef68 100644
> > --- a/arch/x86/Kconfig
> > +++ b/arch/x86/Kconfig
> > @@ -1344,8 +1344,13 @@ config ARCH_SELECT_MEMORY_MODEL
> >   	depends on ARCH_SPARSEMEM_ENABLE
> >   
> >   config ARCH_MEMORY_PROBE
> > -	def_bool y
> > +	bool "Enable sysfs memory/probe interface"
> > +	default n
> >   	depends on X86_64 && MEMORY_HOTPLUG
> > +	help
> > +	  This option enables a sysfs memory/probe interface for testing.
> > +	  See Documentation/memory-hotplug.txt for more information.
> > +	  If you are unsure how to answer this question, answer N.
> >   
> >   config ARCH_PROC_KCORE_TEXT
> >   	def_bool y
> > 
> 
> 


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