linux-kernel - Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel(v1)

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Message-Id: <20100112095848.b2cee1f3.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Tue, 12 Jan 2010 09:58:48 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Andi Kleen <ak@...ux.intel.com>
Cc:	"H. Peter Anvin" <hpa@...nel.org>,
	"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>,
	"y-goto@...fujitsu.com" <y-goto@...fujitsu.com>,
	Dave Hansen <haveblue@...ibm.com>,
	"Wu, Fengguang" <fengguang.wu@...el.com>,
	"x86@...nel.org" <x86@...nel.org>
Subject: Re: [PATCH - resend] Memory-Hotplug: Fix the bug on interface
 /dev/mem for 64-bit kernel(v1)

On Fri, 08 Jan 2010 20:47:54 +0100
Andi Kleen <ak@...ux.intel.com> wrote:

> H. Peter Anvin wrote:
> > On 01/07/2010 07:32 PM, Zheng, Shaohui wrote:
> >> Resend the patch to the mailing-list, the original patch URL is 
> >> http://patchwork.kernel.org/patch/69075/, it is not accepted without comments,
> >> sent it again to review.
> >>
> >> Memory-Hotplug: Fix the bug on interface /dev/mem for 64-bit kernel
> >>
> >> The new added memory can not be access by interface /dev/mem, because we do not
> >>  update the variable high_memory. This patch add a new e820 entry in e820 table,
> >>  and update max_pfn, max_low_pfn and high_memory.
> >>
> >> We add a function update_pfn in file arch/x86/mm/init.c to udpate these
> >>  varibles. Memory hotplug does not make sense on 32-bit kernel, so we did not
> >>  concern it in this function.
> >>
> > 
> > Memory hotplug makes sense on 32-bit kernels, at least in virtual
> > environments.
> 
> No VM currently supports it to my knowledge. They all use traditional
> balooning.
> 
> If someone adds that they can still fix it, but right now fixing it on 64bit
> is the important part.
> 
I wonder...with some modification, memory hotplug (or Mel's page coalescing)
can be used for balloning in MAX_ORDER page size.
I'm sorry if VM' baloon drivers has no fragmentaion problem.

Thanks,
-Kame

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