Re: [PATCH v2 0/5] Allocate memmap from hotadded memory

Michal Hocko
2019-08-01T07:48:41Z

On Thu 01-08-19 09:39:57, Michal Hocko wrote:
> On Thu 01-08-19 09:31:09, David Hildenbrand wrote:
> > On 01.08.19 09:26, David Hildenbrand wrote:
> [...]
> > > I am not sure about the implications of having
> > > pfn_valid()/pfn_present()/pfn_online() return true but accessing it
> > > results in crashes. (suspend, kdump, whatever other technology touches
> > > online memory)
> >
> > (oneidea: we could of course go ahead and mark the pages PG_offline
> > before unmapping the pfn range to work around these issues)
>
> PG_reserved and an elevated reference count should be enough to drive
> any pfn walker out. Pfn walkers shouldn't touch any page unless they
> know and recognize their type.

Btw. this shouldn't be much different from DEBUG_PAGE_ALLOC in
principle. The memory is valid, but not mapped to the kernel virtual
space. Nobody should be really touching it anyway.
--
Michal Hocko
SUSE Labs