From: Nick Piggin <piggin@cyberone.com.au>

Randy has just reported that this fixes up his regression. Its now as good
as test5 in his tests with this patch. He is also seeing quite large
increases (above test5) when IO scheduler barriers are disabled (this patch
doesn't do that). Perhaps something is using them too liberally.

Anyway, this reverts AS back to defaulting to not anticipate IO for a
program that submits its first request (this really hurts find | xargs grep
sort of things).  I am working on something to fix this up properly.  That
can go in after 2.6.0 anyway.