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

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Message-ID: <1374105078.24916.62.camel@misato.fc.hp.com>
Date:	Wed, 17 Jul 2013 17:51:18 -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 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.

Thanks,
-Toshi

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