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    SubjectRe: [RFC] [PATCH 0/5 V2] Huge page backed user-space stacks
    On (05/08/08 09:12), Dave Hansen didst pronounce:
    > On Tue, 2008-08-05 at 12:11 +0100, Mel Gorman wrote:
    > > See, that's great until you start dealing with MAP_SHARED|MAP_ANONYMOUS.
    > > To get that right between children, you end up something very fs-like
    > > when the child needs to fault in a page that is already populated by the
    > > parent. I strongly suspect we end up back at hugetlbfs backing it :/
    >
    > Yeah, but the case I'm worried about is plain anonymous. We already
    > have the fs to back SHARED|ANONYMOUS, and they're not really
    > anonymous. :)
    >
    > This patch *really* needs anonymous pages, and it kinda shoehorns them
    > in with the filesystem. Stacks aren't shared at all, so this is a
    > perfect example of where we can forget the fs, right?
    >

    Ok sure, you could do direct inserts for MAP_PRIVATE as conceptually it
    suits this patch. However, I don't see what you gain. By reusing hugetlbfs,
    we get things like proper reservations which we can do for MAP_PRIVATE these
    days. Again, we could call that sort of thing directly if the reservation
    layer was split out separate from hugetlbfs but I still don't see the gain
    for all that churn.

    What am I missing?

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


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