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

[Lorenzo Stoakes <lstoakes@gmail.com>]

On Tue, Feb 28, 2023 at 04:15:21PM -0800, Frank van der Linden wrote:
> 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
>

Surely userfaultfd is part of this equation too? I definitely think this is a
useful converastion to have, in any case!