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    SubjectRe: PG_zero
    >> And there was no
    >> need of using two quicklists for cold and hot pages, less resources are
    >> wasted by just using the lru ordering to diferentiate from hot/cold
    >> allocations and hot/cold freeing.
    > Not sure if this is wise. Reclaimed pages should definitely be cache
    > cold. Other freeing is assumed cache hot and LRU ordered on the hot
    > list which seems right... but I think you want the cold list for page
    > reclaim, don't you?

    You're completely correct about the hot vs cold, but I don't think that
    precludes what Andrea is suggesting ... merge into one list and use the
    hot/cold ends. Mmmm ... why did we do that? I think it was to stop cold
    allocations from eating into hot pages - we'd prefer them to fall back
    into the buddy instead.

    >> Obvious improvements would be to implement a long_write_zero(ptr)
    >> operation that doesn't pollute the cache. IIRC it exists on the alpha, I
    >> assume it exists on x86/x86-64 too. But that's incremental on top of
    >> this.
    >> It seems stable, I'm running it while writing this.
    >> I guess testing on a memory bound architecture would be more interesting
    >> (more cpus will make it more memory bound somewhat).
    >> Comments welcome.
    > I have the feeling that it might not be worthwhile doing zero on idle.
    > You've got chance of blowing the cache on zeroing pages that won't be
    > used for a while. If you do uncached writes then you've changed the
    > problem to memory bandwidth (I guess doesn't matter much on UP).

    Yeah, we got bugger-all benefit out of it. The only think it might do
    is lower the latency on inital load-spikes, but basically you end up
    paying the cache fetch cost twice. But ... numbers rule - if you can come
    up with something that helps a real macro benchmark, I'll eat my non-existant
    hat ;-)


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