This is pretty large but since it's not eagerly committed to physical
pages, it's probably okay. I'm bumping this after running out of space
for a ProtocolServer profile run :^)
This class works by eagerly allocating 1MB of virtual memory but only
adding physical pages on demand. In other words, when you append to it,
its memory usage will increase by 1 page whenever you append across a
page boundary (4KB.)