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    SubjectRe: [PATCH 00/18] Make common x86 arch area for i386 and x86_64 - Take 2
    On Fri, 16 Mar 2007, David Miller wrote:

    > > It is primarily a performance improvement since the sparsemem table
    > > lookups would no longer be necessary and it also streamlines other
    > > frequent cacheline uses. These page -> page_struct and vice versa
    > > operations are key to the performance of various subsystem among them
    > > the slab allocator.
    >
    > If you set the bit range small enough and don't use sparsemem-extreme,
    > the cost is extremely low considering the flexibility you obtain.

    What flexibility?

    > There are always going to be holes on large systems, there isn't
    > really a way to avoid this given how addressing is done on those
    > machines.

    Virtual mmap allows holes in the same way as page tables do. These
    structures were designed for sparseness. I really do not think we should
    rediscuss the material here that was discussed on linux-mm. The outcome of
    that was that we will introduce virtual memmap to reduce sparsemem
    overhead and to increase flexibility.



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