linux-kernel - Re: [PATCH v3 1/2] memory-hotplug: introduce CONFIG_HAVE_BOOTMEM_INFO_NODE and revert register_page_bootmem_info

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Message-ID: <20130117130509.GE20538@dhcp22.suse.cz>
Date:	Thu, 17 Jan 2013 14:05:09 +0100
From:	Michal Hocko <mhocko@...e.cz>
To:	Lin Feng <linfeng@...fujitsu.com>
Cc:	akpm@...ux-foundation.org, linux-mm@...ck.org, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, jbeulich@...e.com,
	dhowells@...hat.com, wency@...fujitsu.com,
	isimatu.yasuaki@...fujitsu.com, paul.gortmaker@...driver.com,
	laijs@...fujitsu.com, kamezawa.hiroyu@...fujitsu.com,
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	benh@...nel.crashing.org, paulus@...ba.org, schwidefsky@...ibm.com,
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	gregkh@...uxfoundation.org, x86@...nel.org, linux390@...ibm.com,
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	sparclinux@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org, tangchen@...fujitsu.com
Subject: Re: [PATCH v3 1/2] memory-hotplug: introduce
 CONFIG_HAVE_BOOTMEM_INFO_NODE and revert register_page_bootmem_info_node()
 when platform not support

On Thu 17-01-13 18:37:10, Lin Feng wrote:
[...]
> > I am still not sure I understand the relation to MEMORY_HOTREMOVE.
> > Is register_page_bootmem_info_node required/helpful even if
> > !CONFIG_MEMORY_HOTREMOVE?
> From old kenrel's view register_page_bootmem_info_node() is defined in 
> CONFIG_MEMORY_HOTPLUG_SPARSE, it registers some info for 
> memory hotplug/remove. If we don't use MEMORY_HOTPLUG feature, this
> function is empty, we don't need the info at all.
> So this info is not required/helpful if !CONFIG_MEMORY_HOTREMOVE.

OK, then I suggest moving it under CONFIG_MEMORY_HOTREMOVE guards rather
than CONFIG_MEMORY_HOTPLUG.

> > Also, now that I am thinking about that more, maybe it would
> > be cleaner to put the select into arch/x86/Kconfig and do it
> > same as ARCH_ENABLE_MEMORY_{HOTPLUG,HOTREMOVE} (and name it
> > ARCH_HAVE_BOOTMEM_INFO_NODE).
> > 
> Maybe put it in mm/Kconfig is a better choice, because if one day
> someone implements the register_page_bootmem_info_node() for other
> archs they will get some clues here, that's it has been implemented on
> x86_64.
> But I'm not so sure...

My understanding is that doing that in arch code is more appropriate
because it makes the generic code less complicated. But I do not have
any strong opinion on that. Looking at other ARCH_ENABLE_MEMORY_HOTPLUG
and others suggests that we should be consistent with that.

Thanks!
-- 
Michal Hocko
SUSE Labs
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