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    SubjectRe: andrea buffer code (2.2.9-C.gz)
    On Wed, 19 May 1999, Manfred Spraul wrote:

    >I noticed that you added a new spinlock to every memmap_t,
    >i.e. 4 bytes for every 4096 bytes system memory.

    Yes.

    >Is that really required? Have you made any profiling?

    If you want to SMP scale well it's needed (I don't think on a two-way SMP
    is a big issue having a per-memmap spinlock instead of a global spinlock
    but on more powerful machines it can help I think).

    The point is that there we don't need a global spinlock but there we can
    scale far more finegriend on per-page basis. If our approch is to scale
    well as possible in SMP without bother to waste some more kbyte of memory
    the spinlock it's required. You know: to scale better you need to waste
    more memory :-).

    An UP compile done with a not-buggy compiler won't waste a bit of memory
    though.

    >The spinlock is only acquired for a few lines,
    >perhaps one global spinlock would save memory.

    Yes but I am not worried, and being more finegrined in SMP is more fun :-).

    Andrea Arcangeli


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