Message-ID: <20070710155051.GA26249@skynet.ie>
Date:	Tue, 10 Jul 2007 16:50:51 +0100
From:	mel@...net.ie (Mel Gorman)
To:	KAMEZAWA Hiroyuki <kamezawa.hiroyu@...fujitsu.com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>, npiggin@...e.de,
	kenchen@...gle.com, jschopp@...tin.ibm.com, apw@...dowen.org,
	a.p.zijlstra@...llo.nl, y-goto@...fujitsu.com, clameter@....com,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org
Subject: Re: -mm merge plans -- anti-fragmentation

On (10/07/07 20:38), KAMEZAWA Hiroyuki didst pronounce:
> On Tue, 10 Jul 2007 12:12:02 +0100
> mel@...net.ie (Mel Gorman) wrote:
> > > For (2), we need some method for specifing the range we will remove. For doing that,
> > > ZONE seems to be good candidate.  Now we use "kernelcore=" boot option to create
> > > ZONE_MOVABLE by hand.
> > 
> > At the risk of putting you on the spot, do you mind saying whether the
> > grouping pages by mobility and ZONE_MOVABLE patches are going in the
> > direction you want or should something totally different be done? If
> > they are going the right direction, is there anything critical that is
> > missing right now?
> > 
> "grouping pages by mobility and ZONE_MOVABLE" things are what I want. And
> I want to go with them. But I know some people doesn't want to increase #
> of zones. It is my concern. 

I'm not overly keen on increasing the number of zones either but it is a
simplier approach, solves some of the problems and is less intrusive than
grouping pages by mobility so it's a reasonable starting point.

> I know ZONE_MOVABLE works well but there are people who don't want new zone.
> So making ZONE_MOVABLE as configurable will be good thing, as Nick Piggin pointed.
> 

I tested your zone-configurable patch and they appear to work.  Your patch
builds whether ZONE_MOVABLE is available or not and ZONE_MOVABLE is only
available when the config option is set.  It is also considerably cleaner
than the patch I put together for a configurable ZONE_MOVABLE which is too
ugly to live in comparison.

> About my other concerns , see node hotplug (below).
> 
> > > But this is the first step. I know Intel guy posted
> > > his idea to specify Hotpluggable-Memory range in SRAT (by firmware).
> > 
> > There may be additional work required to make this play nicely with
> > ZONE_MOVABLE but it shouldn't be anything fundamental.
> > 
> yes. And I don't know his idea about SRAT is acceped in firmware comunity or not.
> For now, kernelcore= works enough for memory hotplug.
> 

Sounds good.

> > > And I think that
> > > other method may be introduced for node-hotplug. 
> > > 
> > 
> > Same as above really. If the node contains one zone - ZONE_MOVABLE, it
> > would work for unplugging.
> > 
> Our concern on node hotplug is "bootmem" and hashtable , pgdata, memmap etc....
> NUMA initilization (of each arch) includes something complicated.
> But this is not directly related to ZONE_MOVABLE things I think.
> It's node-hotplug problem.
> We are now consdiering hot-add nodes after initcalls().
> 

I don't see off-hand how it's so different from normal memory hot-add
but I'll take your word for it. I'll keep an eye out for patches related
to it.

Thanks

-- 
Mel Gorman
Part-time Phd Student                          Linux Technology Center
University of Limerick                         IBM Dublin Software Lab
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