flush/clear the linux buffer/page cache
To reset your disk caches on recent Linuxes, see this page. Briefly, to drop everything,
echo 3 > /proc/sys/vm/drop_caches . You can run "sync" first to flush dirty pages.
The page warns to run "sync" first, which seems a little scary; what I really want is for it to just drop non-dirty pages, so I can benchmark something with a "cold" disk.
(Posting this in part because it took me a while to find it, so hopefully that subject will help search engines in the future.)
PS: been playing with git. Holy hell is it fast.