Re: [PATCH 02/10] mm/numa: automatically generate node migration order

[David Hildenbrand]

On 14.04.21 10:08, Oscar Salvador wrote:
> On Fri, Apr 09, 2021 at 08:07:08PM -0700, Wei Xu wrote:
> > On Thu, Apr 1, 2021 at 11:35 AM Dave Hansen <dave.hansen@xxxxxxxxxxxxxxx> wrote:
> > > + * When Node 0 fills up, its memory should be migrated to
> > > + * Node 1.  When Node 1 fills up, it should be migrated to
> > > + * Node 2.  The migration path start on the nodes with the
> > > + * processors (since allocations default to this node) and
> > > + * fast memory, progress through medium and end with the
> > > + * slow memory:
> > > + *
> > > + *     0 -> 1 -> 2 -> stop
> > > + *     3 -> 4 -> 5 -> stop
> > > + *
> > > + * This is represented in the node_demotion[] like this:
> > > + *
> > > + *     {  1, // Node 0 migrates to 1
> > > + *        2, // Node 1 migrates to 2
> > > + *       -1, // Node 2 does not migrate
> > > + *        4, // Node 3 migrates to 4
> > > + *        5, // Node 4 migrates to 5
> > > + *       -1} // Node 5 does not migrate
> > > + */
> >
> > In this example, if we want to support multiple nodes as the demotion
> > target of a source node, we can group these nodes into three tiers
> > (classes):
> >
> > fast class:
> > 0 -> {1, 4}  // 1 is the preferred
> > 3 -> {4, 1}  // 4 is the preferred
> >
> > medium class:
> > 1 -> {2, 5}  // 2 is the preferred
> > 4 -> {5, 2}  // 5 is the preferred
> >
> > slow class:
> > 2 -> stop
> > 5 -> stop
>
> Hi Wei Xu,
>
> I have some questions about it
>
> Fast class/memory are pictured as those nodes with CPUs, while Slow class/memory
> are PMEM, right?
> Then, what stands for medium class/memory?

My guest best is that fast class is something like HBM (High Bandwidth 
Memory), medium class is ordinary RAM, slow class is PMEM.

--
Thanks,

David / dhildenb