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    SubjectRe: [PATCH 3/4] Embed zone_id information within the zonelist->zones pointer
    On (09/08/07 18:44), Christoph Lameter didst pronounce:
    > On Fri, 10 Aug 2007, Mel Gorman wrote:
    > > >
    > > > Is this necessary? ZONES_SHIFT is always <= 2 so it will work with
    > > > any pointer. Why disable this for UP?
    > > >
    > >
    > > Caution in case the number of zones increases. There was no guarantee of
    > > zone alignment. It's the same reason I have a BUG_ON in the encode
    > > function so that if we don't catch problems at compile-time, it'll go
    > > BANG in a nice predictable fashion.
    > Caution would lead to a BUG_ON but why the #if? Why exclude UP?

    On x86_64 would have ZONE_DMA, ZONE_DMA32, ZONE_NORMAL, ZONE_HIGHMEM and
    ZONE_MOVABLE. On SMP, that's more than two bits worth and would fail t
    runtime. Well, it should at least I didn't actually try it out.

    However, I accept that the SMP check is less than than ideal. I considered
    comparing it against MAX_NR_ZONES but as it's an enum, it can't be checked
    at compile time. What else would make a better check?

    Mel Gorman
    Part-time Phd Student Linux Technology Center
    University of Limerick IBM Dublin Software Lab
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