[LSF/MM/BPF TOPIC] userspace control of memory management

[Frank van der Linden <fvdl@google.com>]

I propose this discussion topic for LSF/MM/BPF.

In a world where memory topologies are becoming more complicated, is
it still possible to have an approach where the kernel deals with
memory management to everyone's satisfaction?

The answer seemingly has been "not quite", since madvise and mempolicy
exist. With things like cxl.mem coming into existence, a heterogeneous
memory setup will become more common.

The number of madvise options keeps growing. There is now a
process_madvise, and there are proposed extensions for the mempolicy
systemcalls, allowing one process to control the policy of another, as
well. There are exported cgroup interfaces to control reclaim, and
discussions have taken place on explicit control reclaim-as-demotion
to other nodes.

Is this the right approach? If so, would it be a good idea to
optionally provide BPF hooks to control certain behavior, and let
userspace direct things even more? Is that even possible,
performance-wise? Would it make sense to be able to influence the
MGLRU generation process in a more direct way if needed?

I think a discussion about these points would be interesting. Or, I
should say, further discussion.

What do you think?

Thanks,

- Frank