TTM's role in score-based eviction

[Lauri Kasanen]

Hi list, Thomas,

I will be investigating the use of a hotness score for each bo, to
replace the ping-pong causing LRU eviction in radeon*.

The goal is to put all bos that fit in VRAM there, in order of hotness;
a new bo should only be placed there if its hotness score is greater
than the lowest VRAM bo's. Then the lowest-hotness-bos in
VRAM should be evicted until the new bo fits. This should result in a
more stable set with less ping-pong.

Jerome advised that the bo placement should be done entirely outside
TTM. As I'm not (yet) too familiar with that side of the kernel, what is
the opinion of TTM folks?

- Lauri

* github.com/clbr/jamkthesis