How much RAM wrt Active Memory not released?

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Jun 9, 2011
I am stumped.
My system has 2 Gb of RAM, 4 2Tb WD HDDs in a raidz1 configuration.
While doing data migration I observed that if I migrate large files (over 500 Mb) into the raidz1, Active memory stays at about 50 Mb. Quite low actually.
However, if I migrate a large number of small files (10 K to 5 Mb), active memory jumps to 1.5 Gb and stays there.
Now I am assuming that ZFS is maximizing its use of RAM, that would be OK, but why is it gobbling all the available RAM?
My vm.kmem_size is 512 Mb. Anything larger and the BSD kernel panics and dumps.
After reading several posts, I figure I should get my RAM to 4 Gb min. That would be OK. However, why is Active memory not being released after the data migration happened? As far as I can tell ZFS flushes every 30 seconds or so. Active memory should come down quite fast once transfer is done.
Any ideas?
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