zfs discuss - Jun 2008 - Tracking down the causes of a mysteriously shrinking ARC cache?

I have a test Solaris machine with 8 GB of memory. When freshly booted,
the ARC consumes 5 GB (and I would be happy to make it consume more)
and file-level prefetching works great even when I hit the machine with
a lot of simultaneous sequential reads.  But overnight, the ARC has
shrunk to 2 GB (as reported by arcstat.pl) and file-level prefetching
is (as expected at that level) absolutely murdering the performance of
simultaneous sequential reads.

 So: is there any way to find out what is consuming the memory and
causing the ARC to shrink (and/or to reset its target size, since
arcstat.pl reports reports that ''c'', the ARC target size, is
also 2GB)?
I''ve looked at ps, which shows no large processes, I have a ::kmastat
dump from mdb (but I don''t know much about how to read it), top still
reports that the system has 8 GB, and vmstat says that there is 1 GB of
free memory and no paging activity.

 Also, is there any way to force-reset the size of the ARC on a live
system, so I could at least periodically kick its maximum size up to
5 GB or 6 GB or so and hope that it sticks?

 Thanks in advance.

	- cks