Re: [PATCH v5 1/5] mm,memory_hotplug: Allocate memmap from the added memory range

[David Hildenbrand]

On 24.03.21 13:37, Michal Hocko wrote:
> On Wed 24-03-21 13:23:47, David Hildenbrand wrote:
> > On 24.03.21 13:10, Michal Hocko wrote:
> > > On Wed 24-03-21 13:03:29, Michal Hocko wrote:
> > > > On Wed 24-03-21 11:12:59, Oscar Salvador wrote:
> > > [...]
> > >
> > > an additional remark
> > >
> > > > > - online_pages()->move_pfn_range_to_zone(): Accounts for node/zone's spanned pages
> > > > > - online_pages()->zone->present_pages += nr_pages;
> > >
> > > I am pretty sure you shouldn't account vmmemmap pages to the target zone
> > > in some cases - e.g. vmemmap cannot be part of the movable zone, can it?
> > > So this would be yet another special casing. This patch has got it wrong
> > > unless I have missed some special casing.
> >
> > It's a bit unfortunate that we have to discuss the very basic design
> > decisions again.
>
> It would be great to have those basic design decisions layed out in the
> changelog.
>
> > @Oscar, maybe you can share the links where we discussed all this and add
> > some of it to the patch description.
> >
> > I think what we have right here is good enough for an initial version, from
> > where on we can improve things without having to modify calling code.
>
> I have to say I really dislike vmemmap proliferation into
> {on,off}lining. It just doesn't belong there from a layering POV. All
> this code should care about is to hand over pages to the allocator and
> make them visible.

Well, someone has to initialize the vmemmap of the vmemmap pages ( which 
is itself :) ), and as the vemmap does not span complete sections things 
can get very weird as we can only set whole sections online (there was 
more to that, I think it's buried in previous discussions).

> Is that a sufficient concern to nack the whole thing? No, I do not think
> so. But I do not see any particular rush to have this work needs to be
> merged ASAP.

Sure, there is no need to rush (not that I suggested that).

--
Thanks,

David / dhildenb