linux-kernel - Re: The performance and behaviour of the anti-fragmentation related patches

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Message-Id: <20070302145029.d4847577.kamezawa.hiroyu@jp.fujitsu.com>
Date:	Fri, 2 Mar 2007 14:50:29 +0900
From:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	akpm@...ux-foundation.org, balbir@...ibm.com, mel@...net.ie,
	npiggin@...e.de, clameter@...r.sgi.com, mingo@...e.hu,
	jschopp@...tin.ibm.com, arjan@...radead.org, mbligh@...igh.org,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: The performance and behaviour of the anti-fragmentation related
 patches

On Thu, 1 Mar 2007 21:11:58 -0800 (PST)
Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> The whole DRAM power story is a bedtime story for gullible children. Don't 
> fall for it. It's not realistic. The hardware support for it DOES NOT 
> EXIST today, and probably won't for several years. And the real fix is 
> elsewhere anyway (ie people will have to do a FBDIMM-2 interface, which 
> is against the whole point of FBDIMM in the first place, but that's what 
> you get when you ignore power in the first version!).
> 

At first, we have memory hot-add now. So I want to implement hot-removing 
hot-added memory, at least. (in this case, we don't have to write invasive
patches to memory-init-core.)

Our(Fujtisu's) product, ia64-NUMA server, has a feature to offline memory.
It supports dynamic reconfigraion of nodes, node-hoplug.

But there is no *shipped* firmware for hotplug yet. RHEL4 couldn't boot on
such hotplug-supported-firmware...so firmware-team were not in hurry.
It will be shipped after RHEL5 comes.
IMHO, a firmware which supports memory-hot-add are ready to support memory-hot-remove
if OS can handle it.

Note:
I heard embeded people often designs their own memory-power-off control on
embeded Linux. (but it never seems to be posted to the list.) But I don't know
they are interested in generic memory hotremove or not.

Thanks,
-Kame

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