Re: [PATCH] mm/hotplug, x86: Disable ARCH_MEMORY_PROBE by default

[Yasuaki Ishimatsu <isimatu.yasuaki@jp.fujitsu.com>]

(2013/07/18 8:51), Toshi Kani wrote:
> On Wed, 2013-07-17 at 19:33 -0400, KOSAKI Motohiro wrote:
>> On Wed, Jul 17, 2013 at 7:29 PM, Toshi Kani <toshi.kani@hp.com> wrote:
>>> On Wed, 2013-07-17 at 19:22 -0400, KOSAKI Motohiro wrote:
>>>> On Wed, Jul 17, 2013 at 5:45 PM, Toshi Kani <toshi.kani@hp.com> 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, users should not be
>>>>> required to use this interface on x86. This probe interface is also
>>>>> error-prone 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 patch disables CONFIG_ARCH_MEMORY_PROBE by default on x86,
>>>>> and clarifies it in Documentation/memory-hotplug.txt.
>>>>
>>>> Why don't you completely remove it? Who should use this strange interface?
>>>
>>> According to the comment below, this probe interface is used on powerpc.
>>> So, we cannot remove it, but to disable it on x86.
>>
>> I meant x86. Why can't we completely remove ARCH_MEMORY_PROBE section
>> from x86 Kconfig?
>
> Oh, I see what you meant.  I do not expect any need for end-users, but I
> was not sure if someone working on the memory hotplug development might
> use it for fake hot-add testing.  Yes, if you folks do not see any need,
> I will remove it from x86 Kconfig.

I do not think the interface is necessary. So I vote to Kosaki's opinion.

Thanks,
Yasuaki Ishimatsu

>
> Thanks,
> -Toshi
>


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