linux-kernel - Re: [PATCH -mm 13/25] Noreclaim LRU Infrastructure

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Message-Id: <20080610143334.c53d7d8a.akpm@linux-foundation.org>
Date:	Tue, 10 Jun 2008 14:33:34 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Rik van Riel <riel@...hat.com>
Cc:	clameter@....com, linux-kernel@...r.kernel.org,
	lee.schermerhorn@...com, kosaki.motohiro@...fujitsu.com,
	linux-mm@...ck.org, eric.whitney@...com,
	Paul Mundt <lethal@...ux-sh.org>,
	Andi Kleen <andi@...stfloor.org>, Ingo Molnar <mingo@...e.hu>,
	Andy Whitcroft <apw@...dowen.org>
Subject: Re: [PATCH -mm 13/25] Noreclaim LRU Infrastructure

On Tue, 10 Jun 2008 15:37:02 -0400
Rik van Riel <riel@...hat.com> wrote:

> On Tue, 10 Jun 2008 12:17:23 -0700 (PDT)
> Christoph Lameter <clameter@....com> wrote:
> 
> > On Sun, 8 Jun 2008, Andrew Morton wrote:
> > 
> > > And it will take longer to get those problems sorted out if 32-bt
> > > machines aren't even compiing the new code in.
> > 
> > The problem is going to be less if we dependedn on 
> > CONFIG_PAGEFLAGS_EXTENDED instead of 64 bit. This means that only certain 
> > 32bit NUMA/sparsemem configs cannot do this due to lack of page flags.
> > 
> > I did the pageflags rework in part because of Rik's project.
> 
> I think your pageflags work freed up a number of bits on 32
> bit systems, unless someone compiles a 32 bit system with
> support for 4 memory zones (2 bits ZONE_SHIFT) and 64 NUMA
> nodes (6 bits NODE_SHIFT), in which case we should still
> have 24 bits for flags.
> 
> Of course, having 64 NUMA nodes and a ZONE_SHIFT of 2 on
> a 32 bit system is probably total insanity already.  I
> suspect very few people compile 32 bit with NUMA at all,
> except if it is an architecture that uses DISCONTIGMEM
> instead of zones, in which case ZONE_SHIFT is 0, which
> will free up space too :)

Maybe it's time to bite the bullet and kill i386 NUMA support.  afaik
it's just NUMAQ and a 2-node NUMAish machine which IBM made (as400?)

arch/sh uses NUMA for 32-bit, I believe. But I don't know what its
maximum node count is.  The default for sh NODES_SHIFT is 3.  
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