> Arguably, you could say that you don't care if you loose some more Mb
> of VA space, since you don't care if you have, say, another 128Mb less
> at a total of 4Gb. Which is true for normal applications; there may
> be things out there that use a sparsely mapped VA space.

There may be -- well, no, to be more reasonable, there _are_.  However, given
the current choice between supporting very sparsely mapped VA space for some
very rare user programs (look how few people complain about the current
extremely low hard limit on this -- and those who do complain would usually
be satisfied by doubling or quadrupling it) and supporting a reasonably sized
buffer cache for modern disks and memories, the default outght to be in favor
of the latter?

(BTW mixing up where the kernel was mapped ought to teach me to look at the
 _values_ of constants before talking about them, oughtn't it?)

Thor