On Fri, 2007-05-04 at 09:18 -0700, Christoph Lameter wrote:
> On Fri, 4 May 2007, Jesse Barnes wrote:
>
> > I think the idea is to avoid exhausting ZONE_DMA on some NUMA boxes by
> > ordering the fallback list first by zone, then by node distance (e.g.
> > ZONE_NORMAL of local node, then ZONE_NORMAL of next nearest node etc.,
> > followed by ZONE_DMA of local node, ZONE_DMA of next nearest node, etc.).
>
> Maybe it would be cleaner to setup a DMA and DMA32 "node" up and define
> them at a certain distance to the rest of the nodes that only contain
> ZONE_NORMAL (or the zone that is replicated on all nodes). Then we would
> have that effect without reworking zone list generation. Plus in the long
> run we may then be able to get to 1 zone per node avoiding the
> difficulties coming zone fallback altogether.
>
> > Another option would be to make this behavior automatic if both ZONE_DMA
> > and ZONE_NORMAL had pages. I initially wrote this stuff with the idea
> > that machines that really needed it would have all their memory in
> > ZONE_DMA, but obviously that's not the case, so some more smarts are
> > needed.
>
> I think what would work is to first setup nodes that use the highest zone.
> Then add virtual nodes for the lower zones that may only exist on a single
> node.
>
> I.e. a 4 node x86_64 box may have
>
> Node
> 0 ZONE_NORMAL
> 1 ZONE_NORMAL
> 2 ZONE_NORMAL
> 3 ZONE_NORMAL
> 4 ZONE_DMA32
> 5 [additional ZONE_DMA32 if zone DMA32 is split over multiple nodes]
> 6 ZONE_DMA
>
> The SLIT information can be used to control how the nodes fallback to the
> DMA32 nodes on 4 and 5. Node 6 would be given a very high SLIT distance so
> that it would be used only if an actual __GFP_DMA occurs or the system
> really runs into memory difficulties.
Hmmm... "serious hackery", indeed! ;-)
Lee
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