Post any defects you find in the released or beta versions of the ImageMagick software here. Include the ImageMagick version, OS, and any command-line required to reproduce the problem. Got a patch for a bug? Post it here.
the code (and data) is really only occupying one block of shared memory.
Not really. When I use IM 6.2.8 or 6.7.1 (with open-mp disabled) server's load average is about 1-2. When I install 6.7.6-5 server's load average is about 10-50. It doesn't seems to me that it occupies only one block.