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

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Message-ID: <1374256575.24916.176.camel@misato.fc.hp.com>
Date:	Fri, 19 Jul 2013 11:56:15 -0600
From:	Toshi Kani <toshi.kani@...com>
To:	KOSAKI Motohiro <kosaki.motohiro@...il.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	LKML <linux-kernel@...r.kernel.org>, x86@...nel.org,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Tang Chen <tangchen@...fujitsu.com>,
	"vasilis.liaskovitis" <vasilis.liaskovitis@...fitbricks.com>
Subject: Re: [PATCH] mm/hotplug, x86: Disable ARCH_MEMORY_PROBE by default

On Wed, 2013-07-17 at 20:24 -0400, KOSAKI Motohiro wrote:
> On Wed, Jul 17, 2013 at 7:51 PM, Toshi Kani <toshi.kani@...com> 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@...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@...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.
> 
> Then it's ok to submit your patch now.
> 
> Acked-by: KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>

I just sent v2 patch, but did not put your Ack since I did not remove
the option from x86 Kconfig per discussions with Dave.  I'd really
appreciate if you can take a look at the v2 and re-ack it if it still
makes sense to you.

Thanks,
-Toshi

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