* Linus Torvalds [off-list ref] wrote:

quoted

You could do it today, although at a pretty high cost. And you'd have to 
forget about supporting any hardware that really wants contiguous memory 
for DMA (sound cards etc). It just isn't worth it.

Btw, in case it wasn't clear: the cost of these kinds of things in the 
kernel is usually not so much the actual "lookup" (whether with hw 
assist or with another field in the "struct page").

[...]

So remappable kernels are certainly doable, they just have more 
fundamental problems than remappable user space _ever_ has. Both from 
a performance and from a complexity angle.

furthermore, it doesnt bring us any closer to removable RAM. The problem 
is still unsolvable (due to the 'how to do you find live pointers to fix 
up' issue), even if the full kernel VM is 'mapped' at 4K granularity.

	Ingo

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