The list_images() function has no way to pass a list of images to EC2's DescribeImages Action. This means that DescribeImages will always return every image that EC2 knows about, which numbers in the several hundreds. In salt-cloud, this causes the CPU and memory to get pegged every time this call is made:
After patching it in my local copy of the repo, I discovered that a pull req had already been submitted which does a much better job at fixing the issue than I did:
If that pull req were to be merged, it would help out a lot.