Re: the new VMt

From: Ingo Molnar (mingo@elte.hu)
Date: Mon Sep 25 2000 - 11:02:18 EST


On Mon, 25 Sep 2000, Andrea Arcangeli wrote:

> Ingo's point is that the underlined line won't ever happen in the
> first place

please dont misinterpret my point ...

Frankly, how often do we allocate multi-order pages? I've just made quick
statistics wrt. how allocation orders are distributed on a more or less
typical system:

        (ALLOC ORDER)
        0: 167081
        1: 850
        2: 16
        3: 25
        4: 0
        5: 1
        6: 0
        7: 2
        8: 13
        9: 5

ie. 99.45% of all allocations are single-page! 0.50% is the 8kb
task-structure. The rest is 0.05%.

i'm not talking about 4MB contiguous physical allocations having to
succeed on a 8MB box. I'm talking about 99% of the simple allocation
points not having to worry about a NULL pointer. (not checking for NULL is
one of the most common allocation-related bug that beats low-RAM systems.)

        Ingo

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