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Date: Wed, 3 Oct 2001 21:38:07 -0300 (BRST)
From: Rik van Riel <riel@conectiva.com.br>
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To: Rob Landley <landley@trommello.org>
Cc: Alexander Viro <viro@math.psu.edu>, Christoph Hellwig <hch@ns.caldera.de>,
        <linux-kernel@vger.kernel.org>,
        Linus Torvalds <torvalds@transmeta.com>
Subject: Re: Whining about 2.5 (was Re: [PATCH] Re: bug? in using generic
 read/write functions to read/write block devices in 2.4.11-pre2)
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On Wed, 3 Oct 2001, Rob Landley wrote:

> (Oh, and what's the deal with "classzones"?  Linus told Andrea
> classzones were a dumb idea, and we'd regret it when we tried to
> inflict NUMA architecture on 2.5, but then went with Andrea's VM
> anyway, which I thought was based on classzones...  Was that ever
> resolved?  What the problem avoided?  What IS a classzone, anyway?
> I'd be happy to RTFM, if anybody could tell me where TF the M is
> hiding...)

Classzones used to be a superset of the memory zones, so
if you have memory zones A, B and C you'd have classzone
Ac consisting of memory zone A, classzone Bc = {A + B}
and Cc = {A + B + C}.

This gives obvious problems for NUMA, suppose you have 4
nodes with zones 1A, 1B, 1C, 2A, 2B, 2C, 3A, 3B, 3C, 4A,
4B and 4C.  Putting together classzones for these isn't
quite obvious and memory balancing will be complex ;)

Of course, nobody knows the exact definitions of classzones
in the new 2.4 VM since it's completely undocumented; lets
hope Andrea will document his code or we'll see a repeat of
the development chaos we had with the 2.2 VM...

cheers,

Rik
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