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

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Date:	Tue, 10 Jun 2008 15:37:02 -0400
From:	Rik van Riel <riel@...hat.com>
To:	Christoph Lameter <clameter@....com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, lee.schermerhorn@...com,
	kosaki.motohiro@...fujitsu.com, linux-mm@...ck.org,
	eric.whitney@...com
Subject: Re: [PATCH -mm 13/25] Noreclaim LRU Infrastructure

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 :)

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