GDB's bcache improved

[Jim Blandy]

> >     Hash table population: 100%
> >     Median hash chain length: 28
> >     Average hash chain length: 28
> >     Maximum hash chain length: 50
> >   [...]
> 
> 
> These population & chain length numbers look quite bad.  Can the hash
> table not grow?

No --- they don't grow.  :(

I think it's okay for the table population to be high --- that just
means your hash function is doing a good job of distributing objects
across the buckets.  The only assessment that matters is chain length.
But I do agree these chain lengths are not very good.