linux-kernel - Re: [PATCH] acpi memory hotplug, add parameter to disable memory hotplug for kexec

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Date:	Fri, 10 Jan 2014 12:57:50 +0900
From:	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>
To:	Vivek Goyal <vgoyal@...hat.com>,
	Prarit Bhargava <prarit@...hat.com>
CC:	KOSAKI Motohiro <kosaki.motohiro@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	<linux-acpi@...r.kernel.org>, Len Brown <lenb@...nel.org>,
	linux kernel mailing list <linux-kernel@...r.kernel.org>,
	Dave Young <dyoung@...hat.com>,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH] acpi memory hotplug, add parameter to disable memory
 hotplug for kexec

(2014/01/10 6:44), Vivek Goyal wrote:
> On Thu, Jan 09, 2014 at 04:34:16PM -0500, KOSAKI Motohiro wrote:
>> On Thu, Jan 9, 2014 at 10:00 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
>>> On Thu, Jan 09, 2014 at 12:00:29AM +0100, Rafael J. Wysocki wrote:
>>>
>>> [..]
>>>>> The system then panics and the kdump/kexec kernel boots.  During this boot
>>>>> ACPi is initialized and the kernel (as can be seen above)
>>>>
>>>> Which is a bug.  You're not supposed to initialize ACPI twice in a row.
>>>
>>> [CC lkml, kexec mailing list, dave young]
>>>
>>> It is a fresh instance of kernel booting and it is initializing its data
>>> structures fresh. It is *not* re-initializing ACPI in same kernel.
>>>
>>>>> This patchset resolves the problem by adding a kernel parameter,
>>>>> no_memory_hotplug, to disable ACPI memory hotplug.  It can be added by default
>>>>> as a parameter to the kexec/kdump kernel so the kernel boots correctly.
>>>>
>>>> This problem is specific to kexec/kdump, so please don't add *generic* command
>>>> line parameters to address this.
>>>>
>>>
>>> There are other command line options to solve kdump problems. In general
>>> one might want to disable memory hogplug on the fly even if it is compiled
>>> in the kernel. So it can act as a good debugging aid.
>>>
>>> Secondly, it can be specified with memmap=exactmap and mem=X paramters to
>>> make sure no memory is hot added in the system.
>>>
>>> So I can see other usages of this parameter. To me it makes sense to have
>>> a separate command line option to disable memory hotplug feature on the
>>> fly.
>>
>> I'm ok this option. But note, even if this option is specified, SH,
>> Power and S390 still
>> be able to use memory hotplug because their firmware are totally
>> different from ACPI.
>>
>> Maybe, adding acpi prefix provides good clarification.
>

> Makes sense. Something like "acpi_no_memhotplug" or "acpi_disable_memhotplug"
> or something else.

I like Prarit's patch and the boot option name. If it is updated,
I'll test it.

Thanks,
Yasuaki Ishimatsu

>
> Thanks
> Vivek
>
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