Transparent hugepages causes a massive slowdown on one of my systems. It has 64GB of RAM, but it seems the kernel allocator fragments under my workload after a couple of days, resulting in very few >2MB regions free (as per proc buddyinfo) even with >30GB of free ram. This slowed down my KVM boots dramatically (10s -> minutes), and perf top looked like the allocator was spending a lot of cycles repeatedly trying and failing to allocate huge pages.

(I don't want to preallocate hugepages because KVM is only a small part of my workload.)