linux-kernel - Re: [PATCH 1/4] mm: Remove dependency on CONFIG_FLATMEM from online

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Message-ID: <1304371504.30823.45.camel@nimitz>
Date:	Mon, 02 May 2011 14:25:04 -0700
From:	Dave Hansen <dave@...ux.vnet.ibm.com>
To:	Daniel Kiper <dkiper@...-space.pl>
Cc:	ian.campbell@...rix.com, akpm@...ux-foundation.org,
	andi.kleen@...el.com, haicheng.li@...ux.intel.com,
	fengguang.wu@...el.com, jeremy@...p.org, konrad.wilk@...cle.com,
	dan.magenheimer@...cle.com, v.tolstov@...fip.ru, pasik@....fi,
	wdauchy@...il.com, rientjes@...gle.com,
	xen-devel@...ts.xensource.com, linux-kernel@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 1/4] mm: Remove dependency on CONFIG_FLATMEM from
 online_page()

On Mon, 2011-05-02 at 23:19 +0200, Daniel Kiper wrote:
> Memory hotplug code strictly depends on CONFIG_SPARSEMEM.
> It means that code depending on CONFIG_FLATMEM in online_page()
> is never compiled. Remove it because it is not needed anymore.

It's subtle, but I don't think that's true.  We had another hotplug mode
for x86_64 before folks were comfortable turning SPARSEMEM on for the
whole architecture.  It was quite possible to have memory hotplug
without sparsemem in that case.  I think Keith Mannthey did some of that
code if I remember right.

But, I'm not sure how much of that stayed in distros versus made it
upstream.  In any case, you might want to chase down the
X86_64_ACPI_NUMA bit to make sure it can't be used with FLATMEM ever.

config MEMORY_HOTPLUG
        bool "Allow for memory hot-add"
        depends on SPARSEMEM || X86_64_ACPI_NUMA
        depends on HOTPLUG && ARCH_ENABLE_MEMORY_HOTPLUG
        depends on (IA64 || X86 || PPC_BOOK3S_64 || SUPERH || S390)

-- Dave

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