Re: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages

[Andrew Morton <akpm@osdl.org>]

On Thu, 25 Jan 2007 23:44:58 +0000 (GMT)
Mel Gorman <mel@csn.ul.ie> wrote:

> The following 8 patches against 2.6.20-rc4-mm1 create a zone called
> ZONE_MOVABLE

Argh.  These surely get all tangled up with the
make-zones-optional-by-adding-zillions-of-ifdef patches:

deal-with-cases-of-zone_dma-meaning-the-first-zone.patch
introduce-config_zone_dma.patch
optional-zone_dma-in-the-vm.patch
optional-zone_dma-in-the-vm-no-gfp_dma-check-in-the-slab-if-no-config_zone_dma-is-set.patch
optional-zone_dma-in-the-vm-no-gfp_dma-check-in-the-slab-if-no-config_zone_dma-is-set-reduce-config_zone_dma-ifdefs.patch
optional-zone_dma-for-ia64.patch
remove-zone_dma-remains-from-parisc.patch
remove-zone_dma-remains-from-sh-sh64.patch
set-config_zone_dma-for-arches-with-generic_isa_dma.patch
zoneid-fix-up-calculations-for-zoneid_pgshift.patch

My objections to those patches:

- They add zillions of ifdefs

- 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.

- 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++)
		...

- I haven't seen any hard numbers to justify the change.

So I want to drop them all.
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