Re: [RFC 5/8] x86_64 without ZONE_DMA

[Christoph Lameter]

On Sat, 8 Jul 2006, Andi Kleen wrote:

> > The savings are not only from the code paths. The VM itself is cleaner and 
> > the balancing issues are not that troublesome anymore.
> 
> Doesn't help - it has to be fixed anyways for NUMA and other architectures.

Some architectures like ours can run with a single zone since they have 
DMA that works anywhere. Same thing is true for my machines are home and 
at work.
 
> Also in my experience empty zones are not a significant problem for VM
> balancing.

The problem is that the zones are not even empty! We keep 16M in some 
weird ZONE_DMA that barely anyone one uses anymore and add slabs to it 
that are only used by some confused device drivers.

Also the empty zones are still a problem since they have to be scanned 
repeatedly (potentially on each allocation). They waste cachelines and 
result in loops where we could just have straight code.
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