Re: [PATCH 4/5] Light Fragmentation Avoidance V20: 004_percpu

[Paul Jackson <pj@sgi.com>]

Mel wrote:
> -		mark -= mark / 2;			[A]
> +		mark /= 2;				[B]
>  	if (alloc_flags & ALLOC_HARDER)
> -		mark -= mark / 4;			[C]
> +		mark /= 4;				[D]

Why these changes?  For each of [A] - [D] above, if I start with a
value of mark == 33 and recycle that same mark through the above
transformation 16 times, I get the following sequence of values:

 A:  33  17   9   5   3   2   1   1   1   1   1   1   1   1   1   1
 B:  33  16   8   4   2   1   0   0   0   0   0   0   0   0   0   0
 C:  33  25  19  15  12   9   7   6   5   4   3   3   3   3   3   3
 D:  33   8   2   0   0   0   0   0   0   0   0   0   0   0   0   0

Comparing [A] to [B], observe that [A] converges to 1, but [B] to 0,
due to handling the underflow differently.

Comparing [C] to [D], observe that [D] converges to 0, due to the
different underflow, and converges much faster, since it is taking off
3/4's instead of 1/4 each iteration.

I doubt you want this change.

-- 
                  I won't rest till it's the best ...
                  Programmer, Linux Scalability
                  Paul Jackson <pj@sgi.com> 1.925.600.0401
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