Re: Memory management facing a 400Gpbs network link

[Michal Hocko <mhocko@kernel.org>]

On Tue 19-02-19 14:21:50, Cristopher Lameter wrote:
> On Tue, 19 Feb 2019, Michal Hocko wrote:
> 
> > On Tue 12-02-19 18:25:50, Cristopher Lameter wrote:
> > > 400G Infiniband will become available this year. This means that the data
> > > ingest speeds can be higher than the bandwidth of the processor
> > > interacting with its own memory.
> > >
> > > For example a single hardware thread is limited to 20Gbyte/sec whereas the
> > > network interface provides 50Gbytes/sec. These rates can only be obtained
> > > currently with pinned memory.
> > >
> > > How can we evolve the memory management subsystem to operate at higher
> > > speeds with more the comforts of paging and system calls that we are used
> > > to?
> >
> > Realistically, is there anything we _can_ do when the HW is the
> > bottleneck?
> 
> Well the hardware is one problem. The problem that a single core cannot
> handle the full memory bandwidth can be solved by spreading the
> processing of the data to multiple processors. So I think the memory
> subsystem could be aware of that? How do we load balance between cores so
> that we can handle the full bandwidth?

Isn't that something that poeple already do from userspace?

> The other is that the memory needs to be pinned and all sorts of special
> measures and tuning needs to be done to make this actually work. Is there
> any way to simplify this?
> 
> Also the need for page pinning becomes a problem since the majority of the
> memory of a system would need to be pinned. Actually the application seems
> to be doing the memory management then?

I am sorry but this still sounds too vague. There are certainly
possibilities to handle part the MM functionality in the userspace.
But why should we discuss that at the MM track. Do you envision any
in kernel changes that would be needed?
-- 
Michal Hocko
SUSE Labs