elevator_linus is seriously broken wrt accounting. Marcelo recently took
the patch to fix it in 2.4.20-pre, here's the 2.5 equiv.

Right now, we account merges as costly and seeks as not. Only thing that
prevents seek starvation is the aging scan. That is broken, very much
so. This patch fixes that to account merges and inserts differently. A
seek is ELV_LINUS_SEEK_COST more costly than a merge, currently that
define is at '16'. Doing the math on a disk, this sort of makes sense.

Defaults are read latency of 1024, which means 1024 merges or 64 seeks.
Writes are double that.