linux-kernel - Re: [ RESEND PATCH v3] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel

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Date:	Thu, 14 Jan 2010 21:24:51 +0800
From:	Wu Fengguang <fengguang.wu@...el.com>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	"Zheng, Shaohui" <shaohui.zheng@...el.com>,
	"linux-mm@...ck.org" <linux-mm@...ck.org>,
	"akpm@...ux-foundation.org" <akpm@...ux-foundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"ak@...ux.intel.com" <ak@...ux.intel.com>,
	"y-goto@...fujitsu.com" <y-goto@...fujitsu.com>,
	Dave Hansen <haveblue@...ibm.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [ RESEND PATCH v3] Memory-Hotplug: Fix the bug on interface
	/dev/mem for 64-bit kernel

Kame,

On Tue, Jan 12, 2010 at 05:04:33PM +0900, KAMEZAWA Hiroyuki wrote:

> 3 points...
> 1. I think this patch cannot be compiled in archs other than x86. Right ?
>    IOW, please add static inline dummy...

Good catch!

> 2. pgdat->[start,end], totalram_pages etc...are updated at memory hotplug.
>    Please place the hook nearby them.

arch/x86/mm/init_64.c:arch_add_memory() updates max_pfn_mapped, in
this sense it's equally OK to update max_pfn/max_low_pfn etc before
the call to arch_add_memory() ;)

> 3. I recommend you yo use memory hotplug notifier.
>    If it's allowed, it will be cleaner.

Hmm, notifier is for _outsider_ subsystems. It smells a bit
overkill to do notifier _inside_ the hotplug code.

>    It seems there are no strict ordering to update parameters this patch touches.

I tend to agree. That said, it does help keep our mind straight if we do it
in some logical order: max_pfn => max_pfn_mapped => totalram_pages etc.

Thanks,
Fengguang
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