Re: [RFC PATCH 3/3] mm,memory_hotplug: Allocate memmap from the added memory range

[David Hildenbrand]

> > > -	move_pfn_range_to_zone(zone, pfn, nr_pages, NULL, MIGRATE_ISOLATE);
> > > +	move_pfn_range_to_zone(zone, pfn, nr_pages, nr_vmemmap_pages, NULL,
> > > +			       MIGRATE_ISOLATE);
> >
> > As mentioned, I'd suggest properly initializing the memmap here
> >
> > if (nr_vmemmap_pages) {
> > 	move_pfn_range_to_zone(zone, pfn, nr_vmemmap_pages, NULL,
> > 			       MIGRATE_UNMOVABLE);
> > }
> > move_pfn_range_to_zone(zone, valid_start_pfn, valid_nr_pages, NULL,
>
> Sure, agreed.
>
> > > +	if (!support_memmap_on_memory(size))
> > > +		mhp_flags &= ~MEMHP_MEMMAP_ON_MEMORY;
> >
> > Callers (e.g., virtio-mem) might rely on this. We should reject this with
> > -EINVAL and provide a way for callers to test whether this flag is possible.
>
> Uhm, we might want to make "support_memmap_on_memory" public, and
> callers who might want to it use can check its return value?
> Or do you have something else in mind?

Right, a way for callers to check if it's supported. 
"mhp_supports_memmap_on_memory" or sth. like that.

Thanks!

--
Thanks,

David / dhildenb