Re: [RFC 5/8] x86_64 without ZONE_DMA

Christoph Lameter
2006-07-08T01:25:44Z

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.