Meta: Transparent memory offloading

This
Meta blog post by Johannes Weiner and Dan Schatzberg describes a set of
memory-management changes used there that they call 'transparent memory
offloading'.

Transparent Memory Offloading (TMO) is Meta’s solution for
heterogeneous data center environments. It introduces a new Linux
kernel mechanism that measures the lost work due to resource
shortage across CPU, memory, and I/O in real time. Guided by this
information and without any prior application knowledge, TMO
automatically adjusts the amount of memory to offload to a
heterogeneous device, such as compressed memory or an SSD.

The article doesn't say where to find the relevant code, not all of which
is in the mainline kernel (and some of which runs in user space).