Messages in this thread | | | Date | Fri, 26 Jan 2007 11:46:15 -0800 | From | Andrew Morton <> | Subject | Re: [PATCH 0/8] Create ZONE_MOVABLE to partition memory between movable and non-movable pages |
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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.
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