On Mon, Sep 11, 2006 at 03:27:29PM -0700, Christoph Lameter wrote: > Optional ZONE_DMA > > This patch follows up on the earlier work in Andrew's tree to reduce > the number of zones. The patches allow to go to a minimum of 2 zones. > This one allows also to make ZONE_DMA optional and therefore the > number of zones can be reduced to one. > > ZONE_DMA is usually used for ISA DMA devices. Typically modern hardware > does not have any of these anymore. So we frequently do not need > the zone anymore. The presence of an additional zone unnecessarily > complicates VM operations. It must be scanned and balancing logic > must operate in it etc etc. If one has a 1-1 correspondence between > zones and nodes in a NUMA system then various other optimizations > become possible. > > Many systems today (especially 64 bit but also 32 bit machines with less > than 4G of memory) can therefore operate just fine with a single zone. > With a single zone various loops can be optimized away by the > compiler. Many system currently do not place anything in ZONE_DMA. On > most of my systems ZONE_DMA is completely empty. Why constantly look > at an empty zone in /proc/zoneinfo and empty slab in /proc/slabinfo? > Non i386 also frequently have no need for ZONE_DMA and zones stay > empty. > I'm missing something here. On Altix, currently ALL of the memory is reported as being in the DMA zone: % cat /proc/budd* Node 0, zone DMA 3015 116 4 1 ... Node 1, zone DMA 4243 355 15 3 ... Node 2, zone DMA 4384 113 6 4 ... % cat /proc/zoneinfo Node 0, zone DMA pages free 5868 ... The DMA slabs are empty, though. I assume your patch will switch Altix memory to a different zone, but what happens when drivers specify GFP_DMA. -- jack - To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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