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    SubjectRe: [00/17] Large Blocksize Support V3
    Mel Gorman wrote:
    > On (26/04/07 16:50), Nick Piggin didst pronounce:

    >>Fragmentation is the problem. The anti-frag patches don't actually
    >>guarantee anything about fragmentation, and even if they did, then
    >
    >
    > The grouping pages by mobility do not guarantee anything but the memory
    > partition (kernelcore= boot parameter) does give hard guarantees about
    > the amount of memory that is "movable". Of course, the partition requires
    > configuration at boot-time so it's less than ideal but it does give hard
    > guarantees.

    For the hugepages people, I can understand that's a solution. But that's
    the last thing you want to do on a system with a limited amount of memory,
    or a regular Joe's desktop/server.


    > Indeed but then you have to deal with internal fragmentation
    > for pages-larger-than-TLB-page. I'm not saying it's wrong but it does
    > come with it's own set of issues.

    None of them is perfect (the ways to increase the size of pagecache pages,
    that is).

    I think in the long term, TLB page sizes will probably increase a little
    bit... but if a given page size is "good enough" for a CPU, they really
    should be good enough for other hardware. I mean, come on, the CPU's TLB
    has to have a good hit ratio and handle several lookups per cycle with a
    3-cycle latency on 3GHz+ hardware... surely a an IO controller's
    scatter-gather engine or IOMMU that has to do a few lookups per disk IO
    is nowhere near so critical as a CPU's datapath: just add a few more
    entries to it, they've already got hundreds of megs of cache, so that
    isn't an issue either.

    --
    SUSE Labs, Novell Inc.
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