how to recycle Inact memory more aggressively?

In the course of the last year or so the behavior of the vm system
has changed in regard to how aggressively Inact memory is recycled.

My box has 8GB of memory.  At the moment I'm copying 100s of gigabytes
from one file system to another one.

Looking at top I observe that there are about 6GB of Inact memory.
This value hardly changes.  Instead of aggressively recycling the
Inact memory the vm now seems to prefer to swap.

Last year, can't rmember excatly when, the behavior was totally
different.  The vm very aggessively recycled Inact memory and,
even when copying 100s of GB of files, the system hardly swapped.

It seems rather strange to me that the vm happily allows gigbytes
of Inact memory to be present and prefers swapping to recyclincg.

Are there any sysctl's I can set to get the old behavior back?

-- 
Gary Jennejohn