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From: Andrew Morton <akpm@osdl.org>
To: Christoph Lameter <clameter@sgi.com>
Cc: Mel Gorman <mel@csn.ul.ie>,
	linux-mm@kvack.org, linux-kernel@vger.kernel.org,
	Christoph Lameter <clameter@engr.sgi.com>
Subject: Re: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages
Date: Fri, 26 Jan 2007 11:46:15 -0800	[thread overview]
Message-ID: <20070126114615.5aa9e213.akpm@osdl.org> (raw)
In-Reply-To: <Pine.LNX.4.64.0701260751230.6141@schroedinger.engr.sgi.com>

On Fri, 26 Jan 2007 07:56:09 -0800 (PST)
Christoph Lameter <clameter@sgi.com> wrote:

> On Fri, 26 Jan 2007, Andrew Morton wrote:
> 
> > - They add zillions of ifdefs
> 
> They just add a few for ZONE_DMA where we alreaday have similar ifdefs for 
> ZONE_DMA32 and ZONE_HIGHMEM.

I refreshed my memory.  It remains awful.

> > - They make the VM's behaviour diverge between different platforms and
> >   between differen configs on the same platforms, and hence degrade
> >   maintainability and increase complexity.
> 
> They avoid unecessary complexity on platforms. They could be made to work 
> on more platforms with measures to deal with what ZONE_DMA 
> provides in different ways. There are 6 or so platforms that do not need 
> ZONE_DMA at all.

As Mel points out, distros will ship with CONFIG_ZONE_DMA=y, so the number
of machines which will actually benefit from this change is really small. 
And the benefit to those few machines will also, I suspect, be small.

> > - We kicked around some quite different ways of implementing the same
> >   things, but nothing came of it.  iirc, one was to remove the hard-coded
> >   zones altogether and rework all the MM to operate in terms of
> > 
> > 	for (idx = 0; idx < NUMBER_OF_ZONES; idx++)
> > 		...
> 
> Hmmm.. How would that be simpler?

Replace a sprinkle of open-coded ifdefs with a regular code sequence which
everyone uses.  Pretty obvious, I'd thought.

Plus it becoems straightforward to extend this from the present four zones
to a complete 12 zones, which gives use the full set of
ZONE_DMA20,ZONE_DMA21,...,ZONE_DMA32 for those funny devices.

> > - I haven't seen any hard numbers to justify the change.
> 
> I have send you numbers showing significant reductions in code size.

If it isn't in the changelog it doesn't exist.  I guess I didn't copy it
into the changelog.

If the only demonstrable benefit is a saving of a few k of text on a small
number of machines then things are looking very grim, IMO.


  reply	other threads:[~2007-01-26 19:46 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-01-25 23:44 Mel Gorman
2007-01-25 23:45 ` [PATCH 1/8] Add __GFP_MOVABLE for callers to flag allocations that may be migrated Mel Gorman
2007-01-26 12:27   ` Nick Piggin
2007-01-26 13:25     ` Mel Gorman
2007-01-25 23:45 ` [PATCH 2/8] Create the ZONE_MOVABLE zone Mel Gorman
2007-01-26 16:28   ` Christoph Lameter
2007-01-26 16:49     ` Mel Gorman
2007-01-29 17:28     ` Mel Gorman
2007-01-26 17:16   ` Christoph Lameter
2007-01-26 17:24     ` Mel Gorman
2007-01-26 17:25       ` Christoph Lameter
2007-01-26 17:38         ` Mel Gorman
2007-01-29 17:31     ` Mel Gorman
2007-01-25 23:45 ` [PATCH 3/8] Allow huge page allocations to use GFP_HIGH_MOVABLE Mel Gorman
2007-01-26 16:33   ` Christoph Lameter
2007-01-26 16:58     ` Mel Gorman
2007-01-26 17:04       ` Christoph Lameter
2007-01-26 17:20         ` Mel Gorman
2007-01-26 17:22           ` Christoph Lameter
2007-01-26 17:37             ` Mel Gorman
2007-01-26 17:45               ` Christoph Lameter
2007-01-26 17:53                 ` Mel Gorman
2007-01-26 18:20                   ` Christoph Lameter
2007-01-26 20:37                     ` Mel Gorman
2007-01-26 18:35                   ` Chris Friesen
2007-01-26 20:44                     ` Mel Gorman
2007-01-26 21:37                       ` Chris Friesen
2007-01-25 23:46 ` [PATCH 4/8] x86 - Specify amount of kernel memory at boot time Mel Gorman
2007-01-25 23:46 ` [PATCH 5/8] ppc and powerpc " Mel Gorman
2007-01-25 23:46 ` [PATCH 6/8] x86_64 " Mel Gorman
2007-01-25 23:47 ` [PATCH 7/8] ia64 " Mel Gorman
2007-01-25 23:47 ` [PATCH 8/8] Add documentation for additional boot parameter and sysctl Mel Gorman
2007-01-26 11:07 ` [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages Andrew Morton
2007-01-26 14:29   ` Mel Gorman
2007-01-26 16:01     ` Christoph Lameter
2007-01-26 15:56   ` Christoph Lameter
2007-01-26 19:46     ` Andrew Morton [this message]
2007-01-26 19:58       ` Christoph Lameter
2007-01-26 20:27         ` Andrew Morton
2007-01-29 21:54           ` Christoph Lameter
2007-01-29 22:36             ` Andrew Morton
2007-01-29 22:45               ` Christoph Lameter
2007-01-29 22:50                 ` Russell King
2007-01-29 23:37                   ` Christoph Lameter
2007-01-30  0:09                     ` Andrew Morton
2007-01-30  9:53                       ` Peter Zijlstra
2007-02-02  5:27                         ` Christoph Lameter
2007-02-02  5:22                       ` Christoph Lameter
2007-01-26 16:21 ` Christoph Lameter
2007-01-26 16:48   ` Mel Gorman
2007-01-26 17:02     ` Christoph Lameter
2007-01-26 17:20       ` Mel Gorman

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