[v3] __pool_alloc rework

[B. Kosnik]

>	May I suggest a simple but possibly effective way to speed up the
>already fast pool_alloc in the mt-case. Well, if you observe, there is
>only one lock for the pool, while the pool is split up into 128/8 parts.
>So, a speed up could be definitely achieved by keeping one lock for each
>part of the pool right?

Right. I was hoping to do this, but couldn't figure out the linkage bits.

I think I have it now, and have posted a patch which implements this.

-benjamin