On Fri, 26 Jan 2007 07:56:09 -0800 (PST)
Christoph Lameter <[email protected]> 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.
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