Re: the new VMt

Andi Kleen
2000-09-25T16:04:48Z

On Mon, Sep 25, 2000 at 06:02:18PM +0200, Ingo Molnar wrote:
> 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%.

An important exception in 2.2/2.4 is NFS with bigger rsize (will be fixed
in 2.5, but 2.4 does it this way). For an 8K r/wsize you need reliable
(=GFP_ATOMIC) 16K allocations.

Another thing I would worry about are ports with multiple user page sizes in 2.5.
Another ugly case is the x86-64 port which has 4K pages but may likely need
a 16K kernel stack due to the 64bit stack bloat.

-Andi