Re: [PATCH v2 2/3] mm/memory_hotplug: split memmap_on_memory requests across memblocks

[David Hildenbrand]

On 14.08.23 08:45, Huang, Ying wrote:
> "Verma, Vishal L" <vishal.l.verma@xxxxxxxxx> writes:
>
> > On Mon, 2023-07-24 at 13:54 +0800, Huang, Ying wrote:
> > > Vishal Verma <vishal.l.verma@xxxxxxxxx> writes:
> > >
> > > > @@ -2035,12 +2056,38 @@ void try_offline_node(int nid)
> > > >   }
> > > >   EXPORT_SYMBOL(try_offline_node);
> > > >
> > > > -static int __ref try_remove_memory(u64 start, u64 size)
> > > > +static void __ref __try_remove_memory(int nid, u64 start, u64 size,
> > > > +                                    struct vmem_altmap *altmap)
> > > >   {
> > > > -       struct vmem_altmap mhp_altmap = {};
> > > > -       struct vmem_altmap *altmap = NULL;
> > > > -       unsigned long nr_vmemmap_pages;
> > > > -       int rc = 0, nid = NUMA_NO_NODE;
> > > > +       /* remove memmap entry */
> > > > +       firmware_map_remove(start, start + size, "System RAM");
> > >
> > > If mhp_supports_memmap_on_memory(), we will call
> > > firmware_map_add_hotplug() for whole range.  But here we may call
> > > firmware_map_remove() for part of range.  Is it OK?
> >
> > Good point, this is a discrepancy in the add vs remove path. Can the
> > firmware memmap entries be moved up a bit in the add path, and is it
> > okay to create these for each memblock? Or should these be for the
> > whole range? I'm not familiar with the implications. (I've left it as
> > is for v3 for now, but depending on the direction I can update in a
> > future rev).
>
> Cced more firmware map developers and maintainers.
>
> Per my understanding, we should create one firmware memmap entry for
> each memblock.

Ideally we should create it for the whole range, ti limit the ranges. 
But it really only matters for DIMMs; for dax/kmem, we'll not create any 
firmware entries.

--
Cheers,

David / dhildenb