Re: [PATCH v2 0/2] mm: Memory offlining + page isolation cleanups

[David Hildenbrand]

On 22.10.19 11:24, Michal Hocko wrote:
> On Tue 22-10-19 11:17:24, David Hildenbrand wrote:
> > On 22.10.19 11:14, Michal Hocko wrote:
> > > On Tue 22-10-19 10:32:11, David Hildenbrand wrote:
> > > [...]
> > > > E.g., arch/x86/kvm/mmu.c:kvm_is_mmio_pfn()
> > >
> > > Thanks for these references. I am not really familiar with kvm so I
> > > cannot really comment on the specific code but I am wondering why
> > > it simply doesn't check for ZONE_DEVICE explicitly? Also we do care
> > > about holes in RAM (from the early boot), those should be reserved
> > > already AFAIR. So we are left with hotplugged memory with holes and
> > > I am not really sure we should bother with this until there is a clear
> > > usecase in sight.
> >
> > Well, checking for ZONE_DEVICE is only possible if you have an initialized
> > memmap. And that is not guaranteed when you start mapping random stuff into
> > your guest via /dev/mem.
>
> Yes, I can understand that part but checking PageReserved on an
> uninitialized memmap is pointless as well. So if you can test for it you

That's why I add pfn_to_online_page() :)

> can very well test for ZONE_DEVICE as well. PageReserved -> ZONE_DEVICE
> is a terrible assumption.
Indeed, it is. But there are more parts in the kernel that I'll be 
fixing. Stay tuned.

--

Thanks,

David / dhildenb