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

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Date:	Thu, 9 Jan 2014 16:34:16 -0500
From:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Prarit Bhargava <prarit@...hat.com>,
	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

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.
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