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

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Message-ID: <20070302061548.GA13552@linux-sh.org>
Date:	Fri, 2 Mar 2007 15:15:48 +0900
From:	Paul Mundt <lethal@...ux-sh.org>
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	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 Fri, Mar 02, 2007 at 02:50:29PM +0900, KAMEZAWA Hiroyuki wrote:
> 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!).
> > 
> 
> 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.
> 
Yes, this is not that uncommon of a thing. People tend to do this in a
couple of different ways, in some cases the system is too loaded to ever
make doing such a thing at run-time worthwhile, and in those cases these
sorts of things tend to be munged in with the suspend code. Unfortunately
it tends to be quite difficult in practice to keep pages in one place,
so people rely on lame chip-select hacks and limiting the amount of
memory that the kernel treats as RAM instead so it never ends up being an
issue. Having some sort of a balance would certainly be nice, though.
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